diff --git a/bin/phpstan/filtered-functions.stub b/bin/phpstan/filtered-functions.stub
index 410dcc7767..01cb75d5ed 100644
--- a/bin/phpstan/filtered-functions.stub
+++ b/bin/phpstan/filtered-functions.stub
@@ -29,3 +29,43 @@
  * }|null Attachment metadata. Null on failure.
  */
 function wp_get_attachment_metadata( int $attachment_id = 0, bool $unfiltered = false ): ?array {}
+
+/**
+ * Updates the attached file and image meta data when the original image was edited.
+ *
+ * @since 5.3.0
+ * @since 6.0.0 The `$filesize` value was added to the returned array.
+ * @access private
+ *
+ * @phpstan-param array{
+ *     width: int,
+ *     height: int,
+ *     path: string
+ * } $saved_data
+ * @phpstan-param array{
+ *     width: int,
+ *     height: int,
+ *     file: string,
+ *     sizes: array<string, array{ file: string, width: int, height: int, 'mime-type': string }>,
+ *     image_meta: array<string, mixed>,
+ *     filesize: int
+ * } $image_meta
+ * @phpstan-return array{
+ *     width: int,
+ *     height: int,
+ *     file: string,
+ *     sizes: array<string, array{ file: string, width: int, height: int, 'mime-type': string, sources?: array<string, array{ file: string, filesize: int }> }>,
+ *     image_meta: array<string, mixed>,
+ *     filesize: int,
+ *     sources?: array<string, array{ file: string, filesize: int }>,
+ *     has_transparency?: bool,
+ *     dominant_color?: string
+ * }
+ *
+ * @param array  $saved_data    The data returned from WP_Image_Editor after successfully saving an image.
+ * @param string $original_file Path to the original file.
+ * @param array  $image_meta    The image meta data.
+ * @param int    $attachment_id The attachment post ID.
+ * @return array The updated image meta data.
+ */
+function _wp_image_meta_replace_original( $saved_data, $original_file, $image_meta, $attachment_id ): array {}
diff --git a/composer.lock b/composer.lock
index 174cb2a9e3..d012f92337 100644
--- a/composer.lock
+++ b/composer.lock
@@ -334,16 +334,16 @@
         },
         {
             "name": "php-stubs/wordpress-stubs",
-            "version": "v6.5.2",
+            "version": "v6.5.3",
             "source": {
                 "type": "git",
                 "url": "https://github.com/php-stubs/wordpress-stubs.git",
-                "reference": "379f17a90c01498d4c99a0d15aab6e7aa6a2c840"
+                "reference": "e611a83292d02055a25f83291a98fadd0c21e092"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/php-stubs/wordpress-stubs/zipball/379f17a90c01498d4c99a0d15aab6e7aa6a2c840",
-                "reference": "379f17a90c01498d4c99a0d15aab6e7aa6a2c840",
+                "url": "https://api.github.com/repos/php-stubs/wordpress-stubs/zipball/e611a83292d02055a25f83291a98fadd0c21e092",
+                "reference": "e611a83292d02055a25f83291a98fadd0c21e092",
                 "shasum": ""
             },
             "require-dev": {
@@ -375,9 +375,9 @@
             ],
             "support": {
                 "issues": "https://github.com/php-stubs/wordpress-stubs/issues",
-                "source": "https://github.com/php-stubs/wordpress-stubs/tree/v6.5.2"
+                "source": "https://github.com/php-stubs/wordpress-stubs/tree/v6.5.3"
             },
-            "time": "2024-04-14T17:30:14+00:00"
+            "time": "2024-05-08T02:12:31+00:00"
         },
         {
             "name": "phpcompatibility/php-compatibility",
@@ -521,16 +521,16 @@
         },
         {
             "name": "phpcsstandards/phpcsutils",
-            "version": "1.0.10",
+            "version": "1.0.11",
             "source": {
                 "type": "git",
                 "url": "https://github.com/PHPCSStandards/PHPCSUtils.git",
-                "reference": "51609a5b89f928e0c463d6df80eb38eff1eaf544"
+                "reference": "c457da9dabb60eb7106dd5e3c05132b1a6539c6a"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/PHPCSStandards/PHPCSUtils/zipball/51609a5b89f928e0c463d6df80eb38eff1eaf544",
-                "reference": "51609a5b89f928e0c463d6df80eb38eff1eaf544",
+                "url": "https://api.github.com/repos/PHPCSStandards/PHPCSUtils/zipball/c457da9dabb60eb7106dd5e3c05132b1a6539c6a",
+                "reference": "c457da9dabb60eb7106dd5e3c05132b1a6539c6a",
                 "shasum": ""
             },
             "require": {
@@ -605,7 +605,7 @@
                     "type": "open_collective"
                 }
             ],
-            "time": "2024-03-17T23:44:50+00:00"
+            "time": "2024-04-24T11:47:18+00:00"
         },
         {
             "name": "phpstan/extension-installer",
@@ -685,16 +685,16 @@
         },
         {
             "name": "phpstan/phpdoc-parser",
-            "version": "1.28.0",
+            "version": "1.29.0",
             "source": {
                 "type": "git",
                 "url": "https://github.com/phpstan/phpdoc-parser.git",
-                "reference": "cd06d6b1a1b3c75b0b83f97577869fd85a3cd4fb"
+                "reference": "536889f2b340489d328f5ffb7b02bb6b183ddedc"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/phpstan/phpdoc-parser/zipball/cd06d6b1a1b3c75b0b83f97577869fd85a3cd4fb",
-                "reference": "cd06d6b1a1b3c75b0b83f97577869fd85a3cd4fb",
+                "url": "https://api.github.com/repos/phpstan/phpdoc-parser/zipball/536889f2b340489d328f5ffb7b02bb6b183ddedc",
+                "reference": "536889f2b340489d328f5ffb7b02bb6b183ddedc",
                 "shasum": ""
             },
             "require": {
@@ -726,22 +726,22 @@
             "description": "PHPDoc parser with support for nullable, intersection and generic types",
             "support": {
                 "issues": "https://github.com/phpstan/phpdoc-parser/issues",
-                "source": "https://github.com/phpstan/phpdoc-parser/tree/1.28.0"
+                "source": "https://github.com/phpstan/phpdoc-parser/tree/1.29.0"
             },
-            "time": "2024-04-03T18:51:33+00:00"
+            "time": "2024-05-06T12:04:23+00:00"
         },
         {
             "name": "phpstan/phpstan",
-            "version": "1.10.66",
+            "version": "1.10.67",
             "source": {
                 "type": "git",
                 "url": "https://github.com/phpstan/phpstan.git",
-                "reference": "94779c987e4ebd620025d9e5fdd23323903950bd"
+                "reference": "16ddbe776f10da6a95ebd25de7c1dbed397dc493"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/phpstan/phpstan/zipball/94779c987e4ebd620025d9e5fdd23323903950bd",
-                "reference": "94779c987e4ebd620025d9e5fdd23323903950bd",
+                "url": "https://api.github.com/repos/phpstan/phpstan/zipball/16ddbe776f10da6a95ebd25de7c1dbed397dc493",
+                "reference": "16ddbe776f10da6a95ebd25de7c1dbed397dc493",
                 "shasum": ""
             },
             "require": {
@@ -784,13 +784,9 @@
                 {
                     "url": "https://github.com/phpstan",
                     "type": "github"
-                },
-                {
-                    "url": "https://tidelift.com/funding/github/packagist/phpstan/phpstan",
-                    "type": "tidelift"
                 }
             ],
-            "time": "2024-03-28T16:17:31+00:00"
+            "time": "2024-04-16T07:22:02+00:00"
         },
         {
             "name": "phpstan/phpstan-deprecation-rules",
@@ -2082,16 +2078,16 @@
         },
         {
             "name": "squizlabs/php_codesniffer",
-            "version": "3.9.1",
+            "version": "3.9.2",
             "source": {
                 "type": "git",
                 "url": "https://github.com/PHPCSStandards/PHP_CodeSniffer.git",
-                "reference": "267a4405fff1d9c847134db3a3c92f1ab7f77909"
+                "reference": "aac1f6f347a5c5ac6bc98ad395007df00990f480"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/PHPCSStandards/PHP_CodeSniffer/zipball/267a4405fff1d9c847134db3a3c92f1ab7f77909",
-                "reference": "267a4405fff1d9c847134db3a3c92f1ab7f77909",
+                "url": "https://api.github.com/repos/PHPCSStandards/PHP_CodeSniffer/zipball/aac1f6f347a5c5ac6bc98ad395007df00990f480",
+                "reference": "aac1f6f347a5c5ac6bc98ad395007df00990f480",
                 "shasum": ""
             },
             "require": {
@@ -2158,7 +2154,7 @@
                     "type": "open_collective"
                 }
             ],
-            "time": "2024-03-31T21:03:09+00:00"
+            "time": "2024-04-23T20:25:34+00:00"
         },
         {
             "name": "symfony/polyfill-php73",
@@ -2416,16 +2412,16 @@
         },
         {
             "name": "wp-phpunit/wp-phpunit",
-            "version": "6.5.2",
+            "version": "6.5.3",
             "source": {
                 "type": "git",
                 "url": "https://github.com/wp-phpunit/wp-phpunit.git",
-                "reference": "4368fd1dd37d0314cbaa9040be39d835616aeb17"
+                "reference": "ef2cb44c0d991ac0c3a7a3ed0d2d1cf3fe8d8f2f"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/wp-phpunit/wp-phpunit/zipball/4368fd1dd37d0314cbaa9040be39d835616aeb17",
-                "reference": "4368fd1dd37d0314cbaa9040be39d835616aeb17",
+                "url": "https://api.github.com/repos/wp-phpunit/wp-phpunit/zipball/ef2cb44c0d991ac0c3a7a3ed0d2d1cf3fe8d8f2f",
+                "reference": "ef2cb44c0d991ac0c3a7a3ed0d2d1cf3fe8d8f2f",
                 "shasum": ""
             },
             "type": "library",
@@ -2460,7 +2456,7 @@
                 "issues": "https://github.com/wp-phpunit/issues",
                 "source": "https://github.com/wp-phpunit/wp-phpunit"
             },
-            "time": "2024-04-03T00:33:03+00:00"
+            "time": "2024-05-07T16:46:52+00:00"
         },
         {
             "name": "yoast/phpunit-polyfills",
diff --git a/includes/admin/plugins.php b/includes/admin/plugins.php
index 9717e0cc1d..a27c778e9b 100644
--- a/includes/admin/plugins.php
+++ b/includes/admin/plugins.php
@@ -60,6 +60,11 @@ function perflab_query_plugin_info( string $plugin_slug ) {
 
 	set_transient( 'perflab_plugin_info_' . $plugin_slug, $plugin, HOUR_IN_SECONDS );
 
+	/**
+	 * Validated (mostly) plugin data.
+	 *
+	 * @var array{name: string, slug: string, short_description: string, requires: string|false, requires_php: string|false, requires_plugins: string[], download_link: string, version: string} $plugin
+	 */
 	return $plugin;
 }
 
diff --git a/includes/server-timing/class-perflab-server-timing.php b/includes/server-timing/class-perflab-server-timing.php
index 8208c780b2..c190a2fe23 100644
--- a/includes/server-timing/class-perflab-server-timing.php
+++ b/includes/server-timing/class-perflab-server-timing.php
@@ -9,6 +9,11 @@
 /**
  * Class controlling the Server-Timing header.
  *
+ * @phpstan-type MetricArguments array{
+ *                   measure_callback: callable( Perflab_Server_Timing_Metric ): void,
+ *                   access_cap: string
+ *               }
+ *
  * @since 1.8.0
  */
 class Perflab_Server_Timing {
@@ -25,7 +30,8 @@ class Perflab_Server_Timing {
 	 * Map of registered metric slugs and their registered data.
 	 *
 	 * @since 1.8.0
-	 * @var array<string, array{measure_callback: callable, access_cap: string}>
+	 * @phpstan-var array<string, MetricArguments>
+	 * @var array<string, array>
 	 */
 	private $registered_metrics_data = array();
 
@@ -36,8 +42,10 @@ class Perflab_Server_Timing {
 	 *
 	 * @since 1.8.0
 	 *
-	 * @param string                                                $metric_slug The metric slug.
-	 * @param array{measure_callback: callable, access_cap: string} $args        {
+	 * @phpstan-param MetricArguments $args
+	 *
+	 * @param string                         $metric_slug The metric slug.
+	 * @param array<string, callable|string> $args        {
 	 *     Arguments for the metric.
 	 *
 	 *     @type callable $measure_callback The callback that initiates calculating the metric value. It will receive
@@ -94,6 +102,11 @@ public function register_metric( string $metric_slug, array $args ): void {
 			);
 			return;
 		}
+		/**
+		 * Validated args.
+		 *
+		 * @var MetricArguments $args
+		 */
 
 		$this->registered_metrics[ $metric_slug ]      = new Perflab_Server_Timing_Metric( $metric_slug );
 		$this->registered_metrics_data[ $metric_slug ] = $args;
diff --git a/includes/server-timing/defaults.php b/includes/server-timing/defaults.php
index 32d883892c..f242f690f9 100644
--- a/includes/server-timing/defaults.php
+++ b/includes/server-timing/defaults.php
@@ -148,7 +148,7 @@ static function ( $passthrough = null ) {
 			perflab_server_timing_register_metric(
 				'template',
 				array(
-					'measure_callback' => static function ( $metric ): void {
+					'measure_callback' => static function ( Perflab_Server_Timing_Metric $metric ): void {
 						$metric->measure_before();
 						add_action( 'perflab_server_timing_send_header', array( $metric, 'measure_after' ), PHP_INT_MAX );
 					},
diff --git a/includes/server-timing/load.php b/includes/server-timing/load.php
index 6ae7a0bc2a..3c1ede6995 100644
--- a/includes/server-timing/load.php
+++ b/includes/server-timing/load.php
@@ -205,7 +205,7 @@ function perflab_sanitize_server_timing_setting( $value ): array {
 			array_unique(
 				array_filter(
 					array_map(
-						static function ( $hook_name ) {
+						static function ( string $hook_name ): string {
 							/*
 							 * Allow any characters except whitespace.
 							 * While most hooks use a limited set of characters, hook names in plugins are not
@@ -227,5 +227,10 @@ static function ( $hook_name ) {
 
 	$value['output_buffering'] = (bool) $value['output_buffering'];
 
+	/**
+	 * Validated value.
+	 *
+	 * @var array{benchmarking_actions: string[], benchmarking_filters: string[], output_buffering: bool} $value
+	 */
 	return $value;
 }
diff --git a/includes/site-health/audit-enqueued-assets/helper.php b/includes/site-health/audit-enqueued-assets/helper.php
index e0088c918a..ae826fd53a 100644
--- a/includes/site-health/audit-enqueued-assets/helper.php
+++ b/includes/site-health/audit-enqueued-assets/helper.php
@@ -22,7 +22,8 @@ function perflab_aea_enqueued_js_assets_test(): array {
 	 * If the test didn't run yet, deactivate.
 	 */
 	$enqueued_scripts = perflab_aea_get_total_enqueued_scripts();
-	if ( false === $enqueued_scripts ) {
+	$bytes_enqueued   = perflab_aea_get_total_size_bytes_enqueued_scripts();
+	if ( false === $enqueued_scripts || false === $bytes_enqueued ) {
 		// The return value is validated in JavaScript at:
 		// <https://github.com/WordPress/wordpress-develop/blob/d1e0a6241dcc34f4a5ed464a741116461a88d43b/src/js/_enqueues/admin/site-health.js#L65-L114>
 		// If the value lacks the required keys of test, label, and description then it is omitted.
@@ -48,7 +49,7 @@ function perflab_aea_enqueued_js_assets_test(): array {
 						'performance-lab'
 					),
 					$enqueued_scripts,
-					size_format( perflab_aea_get_total_size_bytes_enqueued_scripts() )
+					size_format( $bytes_enqueued )
 				)
 			)
 		),
@@ -74,7 +75,7 @@ function perflab_aea_enqueued_js_assets_test(): array {
 	 */
 	$scripts_size_threshold = apply_filters( 'perflab_aea_enqueued_scripts_byte_size_threshold', 300000 );
 
-	if ( $enqueued_scripts > $scripts_threshold || perflab_aea_get_total_size_bytes_enqueued_scripts() > $scripts_size_threshold ) {
+	if ( $enqueued_scripts > $scripts_threshold || $bytes_enqueued > $scripts_size_threshold ) {
 		$result['status'] = 'recommended';
 
 		$result['description'] = sprintf(
@@ -89,7 +90,7 @@ function perflab_aea_enqueued_js_assets_test(): array {
 						'performance-lab'
 					),
 					$enqueued_scripts,
-					size_format( perflab_aea_get_total_size_bytes_enqueued_scripts() )
+					size_format( $bytes_enqueued )
 				)
 			)
 		);
@@ -117,7 +118,8 @@ function perflab_aea_enqueued_js_assets_test(): array {
 function perflab_aea_enqueued_css_assets_test(): array {
 	// Omit if the test didn't run yet, omit.
 	$enqueued_styles = perflab_aea_get_total_enqueued_styles();
-	if ( false === $enqueued_styles ) {
+	$bytes_enqueued  = perflab_aea_get_total_size_bytes_enqueued_styles();
+	if ( false === $enqueued_styles || false === $bytes_enqueued ) {
 		// The return value is validated in JavaScript at:
 		// <https://github.com/WordPress/wordpress-develop/blob/d1e0a6241dcc34f4a5ed464a741116461a88d43b/src/js/_enqueues/admin/site-health.js#L65-L114>
 		// If the value lacks the required keys of test, label, and description then it is omitted.
@@ -142,7 +144,7 @@ function perflab_aea_enqueued_css_assets_test(): array {
 						'performance-lab'
 					),
 					$enqueued_styles,
-					size_format( perflab_aea_get_total_size_bytes_enqueued_styles() )
+					size_format( $bytes_enqueued )
 				)
 			)
 		),
@@ -182,7 +184,7 @@ function perflab_aea_enqueued_css_assets_test(): array {
 						'performance-lab'
 					),
 					$enqueued_styles,
-					size_format( perflab_aea_get_total_size_bytes_enqueued_styles() )
+					size_format( $bytes_enqueued )
 				)
 			)
 		);
@@ -210,7 +212,7 @@ function perflab_aea_enqueued_css_assets_test(): array {
 function perflab_aea_get_total_enqueued_scripts() {
 	$enqueued_scripts      = false;
 	$list_enqueued_scripts = get_transient( 'aea_enqueued_front_page_scripts' );
-	if ( $list_enqueued_scripts ) {
+	if ( is_array( $list_enqueued_scripts ) ) {
 		$enqueued_scripts = count( $list_enqueued_scripts );
 	}
 	return $enqueued_scripts;
@@ -226,10 +228,12 @@ function perflab_aea_get_total_enqueued_scripts() {
 function perflab_aea_get_total_size_bytes_enqueued_scripts() {
 	$total_size            = false;
 	$list_enqueued_scripts = get_transient( 'aea_enqueued_front_page_scripts' );
-	if ( $list_enqueued_scripts ) {
+	if ( is_array( $list_enqueued_scripts ) ) {
 		$total_size = 0;
 		foreach ( $list_enqueued_scripts as $enqueued_script ) {
-			$total_size += $enqueued_script['size'];
+			if ( is_array( $enqueued_script ) && array_key_exists( 'size', $enqueued_script ) && is_int( $enqueued_script['size'] ) ) {
+				$total_size += $enqueued_script['size'];
+			}
 		}
 	}
 	return $total_size;
@@ -261,10 +265,12 @@ function perflab_aea_get_total_enqueued_styles() {
 function perflab_aea_get_total_size_bytes_enqueued_styles() {
 	$total_size           = false;
 	$list_enqueued_styles = get_transient( 'aea_enqueued_front_page_styles' );
-	if ( $list_enqueued_styles ) {
+	if ( is_array( $list_enqueued_styles ) ) {
 		$total_size = 0;
 		foreach ( $list_enqueued_styles as $enqueued_style ) {
-			$total_size += $enqueued_style['size'];
+			if ( is_array( $enqueued_style ) && array_key_exists( 'size', $enqueued_style ) && is_int( $enqueued_style['size'] ) ) {
+				$total_size += $enqueued_style['size'];
+			}
 		}
 	}
 	return $total_size;
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
index 31e9b13aab..31962d0e39 100644
--- a/phpstan.neon.dist
+++ b/phpstan.neon.dist
@@ -1,7 +1,7 @@
 includes:
 	- phar://phpstan.phar/conf/bleedingEdge.neon
 parameters:
-	level: 6
+	level: 7
 	treatPhpDocTypesAsCertain: false
 	paths:
 		- load.php
@@ -23,3 +23,41 @@ parameters:
 		- bin/phpstan/filtered-functions.stub
 	dynamicConstantNames:
 		- PERFLAB_OBJECT_CACHE_DROPIN_VERSION
+	ignoreErrors:
+		-
+			# Ignore error related to PHP 8 using a GdImage but PHP 7 using a resource.
+			message: '/^Parameter .+? of function .+? expects resource, GdImage\|resource given\.$/'
+			path: plugins/dominant-color-images/*.php
+
+		# The following ignored errors are all for tests. They are likely excessively strict and do not warrant being fixed.
+		# TODO: Use error identifiers instead of messages once PHPStan 1.11 is out: <https://github.com/WordPress/performance/issues/1209>.
+		-
+			message: '/Parameter #\d.+given./'
+			path: tests/*
+		-
+			message: '/Cannot use array destructuring/'
+			path: tests/*
+		-
+			message: '/Call to an undefined method/'
+			path: tests/*
+		-
+			message: '/Offset .+ might not exist on array/'
+			path: tests/*
+		-
+			message: '/Part .+ of encapsed string cannot be cast to string/'
+			path: tests/*
+		-
+			message: '/Possibly invalid array key type/'
+			path: tests/*
+		-
+			message: '/Static property .+ does not accept .+/'
+			path: tests/*
+		-
+			message: '/Cannot call method format\(\) on DateTimeImmutable\|false/'
+			path: tests/*
+		-
+			message: '/Property .+ does not accept array.+/'
+			path: tests/*
+		-
+			message: '/Cannot cast .+ to string/'
+			path: tests/*
diff --git a/plugins/dominant-color-images/class-dominant-color-image-editor-gd.php b/plugins/dominant-color-images/class-dominant-color-image-editor-gd.php
index 5468198dee..a6106bf1f6 100644
--- a/plugins/dominant-color-images/class-dominant-color-image-editor-gd.php
+++ b/plugins/dominant-color-images/class-dominant-color-image-editor-gd.php
@@ -32,7 +32,12 @@ public function get_dominant_color() {
 		}
 		// The logic here is resize the image to 1x1 pixel, then get the color of that pixel.
 		$shorted_image = imagecreatetruecolor( 1, 1 );
-		imagecopyresampled( $shorted_image, $this->image, 0, 0, 0, 0, 1, 1, imagesx( $this->image ), imagesy( $this->image ) );
+		$image_width   = imagesx( $this->image );
+		$image_height  = imagesy( $this->image );
+		if ( false === $shorted_image || false === $image_width || false === $image_height ) {
+			return new WP_Error( 'image_editor_dominant_color_error', __( 'Dominant color detection failed.', 'dominant-color-images' ) );
+		}
+		imagecopyresampled( $shorted_image, $this->image, 0, 0, 0, 0, 1, 1, $image_width, $image_height );
 
 		$rgb = imagecolorat( $shorted_image, 0, 0 );
 		if ( false === $rgb ) {
@@ -49,7 +54,6 @@ public function get_dominant_color() {
 		return $hex;
 	}
 
-
 	/**
 	 * Looks for transparent pixels in the image.
 	 * If there are none, it returns false.
@@ -69,8 +73,14 @@ public function has_transparency() {
 		$h = imagesy( $this->image );
 		for ( $x = 0; $x < $w; $x++ ) {
 			for ( $y = 0; $y < $h; $y++ ) {
-				$rgb  = imagecolorat( $this->image, $x, $y );
+				$rgb = imagecolorat( $this->image, $x, $y );
+				if ( false === $rgb ) {
+					return new WP_Error( 'unable_to_obtain_rgb_via_imagecolorat' );
+				}
 				$rgba = imagecolorsforindex( $this->image, $rgb );
+				if ( ! is_array( $rgba ) ) {
+					return new WP_Error( 'unable_to_obtain_rgba_via_imagecolorsforindex' );
+				}
 				if ( $rgba['alpha'] > 0 ) {
 					return true;
 				}
diff --git a/plugins/dominant-color-images/helper.php b/plugins/dominant-color-images/helper.php
index b723250ece..ab5b1a5374 100644
--- a/plugins/dominant-color-images/helper.php
+++ b/plugins/dominant-color-images/helper.php
@@ -57,6 +57,9 @@ function dominant_color_get_dominant_color_data( int $attachment_id ) {
 	if ( ! $file ) {
 		$file = get_attached_file( $attachment_id );
 	}
+	if ( ! $file ) {
+		return new WP_Error( 'no_image_found', __( 'Unable to load image.', 'dominant-color-images' ) );
+	}
 	add_filter( 'wp_image_editors', 'dominant_color_set_image_editors' );
 
 	/**
@@ -119,6 +122,9 @@ function dominant_color_get_attachment_file_path( int $attachment_id, string $si
 	}
 
 	$file = get_attached_file( $attachment_id );
+	if ( ! $file ) {
+		return false;
+	}
 
 	$filepath = str_replace( wp_basename( $file ), $imagedata['sizes'][ $size ]['file'], $file );
 
diff --git a/plugins/embed-optimizer/hooks.php b/plugins/embed-optimizer/hooks.php
index 8625f814a9..2c54afdf60 100644
--- a/plugins/embed-optimizer/hooks.php
+++ b/plugins/embed-optimizer/hooks.php
@@ -81,7 +81,7 @@ function embed_optimizer_filter_oembed_html( string $html ): string {
 			// by preventing links in the hidden iframe from receiving focus.
 			if ( $html_processor->has_class( 'wp-embedded-content' ) ) {
 				$style = $html_processor->get_attribute( 'style' );
-				if ( $style ) {
+				if ( is_string( $style ) ) {
 					// WordPress core injects this clip CSS property:
 					// <https://github.com/WordPress/wordpress-develop/blob/6974b994de5/src/wp-includes/embed.php#L968>.
 					$style = str_replace( 'clip: rect(1px, 1px, 1px, 1px);', 'visibility: hidden;', $style );
diff --git a/plugins/optimization-detective/class-od-html-tag-walker.php b/plugins/optimization-detective/class-od-html-tag-walker.php
index 735dffd3d7..9f7092499e 100644
--- a/plugins/optimization-detective/class-od-html-tag-walker.php
+++ b/plugins/optimization-detective/class-od-html-tag-walker.php
@@ -220,7 +220,7 @@ public function open_tags(): Generator {
 				if ( in_array( $tag_name, self::P_CLOSING_TAGS, true ) ) {
 					$i = array_search( 'P', $this->open_stack_tags, true );
 					if ( false !== $i ) {
-						array_splice( $this->open_stack_tags, $i );
+						array_splice( $this->open_stack_tags, (int) $i );
 						array_splice( $this->open_stack_indices, count( $this->open_stack_tags ) );
 					}
 				}
diff --git a/plugins/optimization-detective/class-od-url-metrics-group-collection.php b/plugins/optimization-detective/class-od-url-metrics-group-collection.php
index a45ac011f5..4fa247c7c6 100644
--- a/plugins/optimization-detective/class-od-url-metrics-group-collection.php
+++ b/plugins/optimization-detective/class-od-url-metrics-group-collection.php
@@ -38,7 +38,12 @@ final class OD_URL_Metrics_Group_Collection implements Countable, IteratorAggreg
 	/**
 	 * Breakpoints in max widths.
 	 *
-	 * Valid values are from 1 to PHP_INT_MAX.
+	 * Valid values are from 1 to PHP_INT_MAX - 1. This is because:
+	 *
+	 * 1. It doesn't make sense for there to be a viewport width of zero, so the first breakpoint (max width) must be at least 1.
+	 * 2. After the last breakpoint, the final breakpoint group is set to be spanning one plus the last breakpoint max width up
+	 *    until PHP_INT_MAX. So a breakpoint cannot be PHP_INT_MAX because then the minimum viewport width for the final group
+	 *    would end up being larger than PHP_INT_MAX.
 	 *
 	 * @var int[]
 	 * @phpstan-var positive-int[]
@@ -78,7 +83,7 @@ public function __construct( array $url_metrics, array $breakpoints, int $sample
 		sort( $breakpoints );
 		$breakpoints = array_values( array_unique( $breakpoints, SORT_NUMERIC ) );
 		foreach ( $breakpoints as $breakpoint ) {
-			if ( $breakpoint <= 1 || PHP_INT_MAX === $breakpoint ) {
+			if ( ! is_int( $breakpoint ) || $breakpoint < 1 || PHP_INT_MAX === $breakpoint ) {
 				throw new InvalidArgumentException(
 					esc_html(
 						sprintf(
@@ -93,6 +98,11 @@ public function __construct( array $url_metrics, array $breakpoints, int $sample
 				);
 			}
 		}
+		/**
+		 * Validated breakpoints.
+		 *
+		 * @var positive-int[] $breakpoints
+		 */
 		$this->breakpoints = $breakpoints;
 
 		// Set sample size.
@@ -133,6 +143,8 @@ public function __construct( array $url_metrics, array $breakpoints, int $sample
 	/**
 	 * Create groups.
 	 *
+	 * @phpstan-return non-empty-array<OD_URL_Metrics_Group>
+	 *
 	 * @return OD_URL_Metrics_Group[] Groups.
 	 */
 	private function create_groups(): array {
diff --git a/plugins/optimization-detective/optimization.php b/plugins/optimization-detective/optimization.php
index 60c7e104b7..f24957ebf6 100644
--- a/plugins/optimization-detective/optimization.php
+++ b/plugins/optimization-detective/optimization.php
@@ -195,7 +195,7 @@ function od_is_response_html_content_type(): bool {
 	);
 	foreach ( $headers_list as $header ) {
 		$header_parts = preg_split( '/\s*[:;]\s*/', strtolower( $header ) );
-		if ( count( $header_parts ) >= 2 && 'content-type' === $header_parts[0] ) {
+		if ( is_array( $header_parts ) && count( $header_parts ) >= 2 && 'content-type' === $header_parts[0] ) {
 			$is_html_content_type = in_array( $header_parts[1], array( 'text/html', 'application/xhtml+xml' ), true );
 		}
 	}
@@ -279,7 +279,7 @@ function od_optimize_template_output_buffer( string $buffer ): string {
 			&&
 			$walker->get_attribute( 'src' )
 			&&
-			! str_starts_with( $walker->get_attribute( 'src' ), 'data:' )
+			! str_starts_with( (string) $walker->get_attribute( 'src' ), 'data:' )
 		);
 
 		/*
@@ -295,7 +295,7 @@ function od_optimize_template_output_buffer( string $buffer ): string {
 		if (
 			$style
 			&&
-			preg_match( '/background(-image)?\s*:[^;]*?url\(\s*[\'"]?(?<background_image>.+?)[\'"]?\s*\)/', $style, $matches )
+			preg_match( '/background(-image)?\s*:[^;]*?url\(\s*[\'"]?(?<background_image>.+?)[\'"]?\s*\)/', (string) $style, $matches )
 			&&
 			! str_starts_with( $matches['background_image'], 'data:' )
 		) {
@@ -342,16 +342,20 @@ function od_optimize_template_output_buffer( string $buffer ): string {
 				$img_attributes = array();
 				foreach ( array( 'src', 'srcset', 'sizes', 'crossorigin' ) as $attr_name ) {
 					$value = $walker->get_attribute( $attr_name );
-					if ( null !== $value ) {
+					if ( is_string( $value ) ) {
 						$img_attributes[ $attr_name ] = $value;
 					}
 				}
 				foreach ( $lcp_element_minimum_viewport_widths_by_xpath[ $xpath ] as $minimum_viewport_width ) {
-					$lcp_elements_by_minimum_viewport_widths[ $minimum_viewport_width ]['img_attributes'] = $img_attributes;
+					if ( is_array( $lcp_elements_by_minimum_viewport_widths[ $minimum_viewport_width ] ) ) {
+						$lcp_elements_by_minimum_viewport_widths[ $minimum_viewport_width ]['img_attributes'] = $img_attributes;
+					}
 				}
 			} elseif ( $background_image_url ) {
 				foreach ( $lcp_element_minimum_viewport_widths_by_xpath[ $xpath ] as $minimum_viewport_width ) {
-					$lcp_elements_by_minimum_viewport_widths[ $minimum_viewport_width ]['background_image'] = $background_image_url;
+					if ( is_array( $lcp_elements_by_minimum_viewport_widths[ $minimum_viewport_width ] ) ) {
+						$lcp_elements_by_minimum_viewport_widths[ $minimum_viewport_width ]['background_image'] = $background_image_url;
+					}
 				}
 			}
 		}
diff --git a/plugins/optimization-detective/storage/class-od-url-metrics-post-type.php b/plugins/optimization-detective/storage/class-od-url-metrics-post-type.php
index 1494b51d0b..38d34c948d 100644
--- a/plugins/optimization-detective/storage/class-od-url-metrics-post-type.php
+++ b/plugins/optimization-detective/storage/class-od-url-metrics-post-type.php
@@ -154,6 +154,7 @@ static function ( $url_metric_data ) use ( $trigger_warning ) {
 						}
 
 						try {
+							// @phpstan-ignore-next-line -- Invalid data will be validated in the constructor.
 							return new OD_URL_Metric( $url_metric_data );
 						} catch ( OD_Data_Validation_Exception $e ) {
 							$trigger_warning(
@@ -225,6 +226,9 @@ static function ( OD_URL_Metric $url_metric ): array {
 			),
 			JSON_UNESCAPED_SLASHES // No need for escaped slashes since not printed to frontend.
 		);
+		if ( ! is_string( $post_data['post_content'] ) ) {
+			return new WP_Error( 'json_encode_error', json_last_error_msg() );
+		}
 
 		$has_kses = false !== has_filter( 'content_save_pre', 'wp_filter_post_kses' );
 		if ( $has_kses ) {
@@ -290,7 +294,7 @@ public static function delete_stale_posts(): void {
 		);
 
 		foreach ( $query->posts as $post ) {
-			if ( self::SLUG === $post->post_type ) { // Sanity check.
+			if ( $post instanceof WP_Post && self::SLUG === $post->post_type ) { // Sanity check.
 				wp_delete_post( $post->ID, true );
 			}
 		}
diff --git a/plugins/optimization-detective/storage/data.php b/plugins/optimization-detective/storage/data.php
index 44d372702b..b94b7fc8cc 100644
--- a/plugins/optimization-detective/storage/data.php
+++ b/plugins/optimization-detective/storage/data.php
@@ -137,7 +137,7 @@ function od_get_current_url(): string {
  * @return string Slug.
  */
 function od_get_url_metrics_slug( array $query_vars ): string {
-	return md5( wp_json_encode( $query_vars ) );
+	return md5( (string) wp_json_encode( $query_vars ) );
 }
 
 /**
diff --git a/plugins/optimization-detective/storage/rest-api.php b/plugins/optimization-detective/storage/rest-api.php
index 106d859e63..8dddf776c8 100644
--- a/plugins/optimization-detective/storage/rest-api.php
+++ b/plugins/optimization-detective/storage/rest-api.php
@@ -130,6 +130,7 @@ function od_handle_rest_request( WP_REST_Request $request ) {
 	try {
 		$properties = OD_URL_Metric::get_json_schema()['properties'];
 		$url_metric = new OD_URL_Metric(
+			// @phpstan-ignore-next-line -- Array shape is validated by the constructor.
 			array_merge(
 				wp_array_slice_assoc(
 					$request->get_params(),
diff --git a/plugins/speculation-rules/class-plsr-url-pattern-prefixer.php b/plugins/speculation-rules/class-plsr-url-pattern-prefixer.php
index be34cfca3c..50fb70a864 100644
--- a/plugins/speculation-rules/class-plsr-url-pattern-prefixer.php
+++ b/plugins/speculation-rules/class-plsr-url-pattern-prefixer.php
@@ -107,13 +107,13 @@ public function prefix_path_pattern( string $path_pattern, string $context = 'ho
 	 */
 	public static function get_default_contexts(): array {
 		return array(
-			'home'       => self::escape_pattern_string( trailingslashit( wp_parse_url( home_url( '/' ), PHP_URL_PATH ) ) ),
-			'site'       => self::escape_pattern_string( trailingslashit( wp_parse_url( site_url( '/' ), PHP_URL_PATH ) ) ),
-			'uploads'    => self::escape_pattern_string( trailingslashit( wp_parse_url( wp_upload_dir( null, false )['baseurl'], PHP_URL_PATH ) ) ),
-			'content'    => self::escape_pattern_string( trailingslashit( wp_parse_url( content_url(), PHP_URL_PATH ) ) ),
-			'plugins'    => self::escape_pattern_string( trailingslashit( wp_parse_url( plugins_url(), PHP_URL_PATH ) ) ),
-			'template'   => self::escape_pattern_string( trailingslashit( wp_parse_url( get_stylesheet_directory_uri(), PHP_URL_PATH ) ) ),
-			'stylesheet' => self::escape_pattern_string( trailingslashit( wp_parse_url( get_template_directory_uri(), PHP_URL_PATH ) ) ),
+			'home'       => self::escape_pattern_string( trailingslashit( (string) wp_parse_url( home_url( '/' ), PHP_URL_PATH ) ) ),
+			'site'       => self::escape_pattern_string( trailingslashit( (string) wp_parse_url( site_url( '/' ), PHP_URL_PATH ) ) ),
+			'uploads'    => self::escape_pattern_string( trailingslashit( (string) wp_parse_url( wp_upload_dir( null, false )['baseurl'], PHP_URL_PATH ) ) ),
+			'content'    => self::escape_pattern_string( trailingslashit( (string) wp_parse_url( content_url(), PHP_URL_PATH ) ) ),
+			'plugins'    => self::escape_pattern_string( trailingslashit( (string) wp_parse_url( plugins_url(), PHP_URL_PATH ) ) ),
+			'template'   => self::escape_pattern_string( trailingslashit( (string) wp_parse_url( get_stylesheet_directory_uri(), PHP_URL_PATH ) ) ),
+			'stylesheet' => self::escape_pattern_string( trailingslashit( (string) wp_parse_url( get_template_directory_uri(), PHP_URL_PATH ) ) ),
 		);
 	}
 
diff --git a/plugins/speculation-rules/helper.php b/plugins/speculation-rules/helper.php
index 758a72f6e6..ef0b8082fd 100644
--- a/plugins/speculation-rules/helper.php
+++ b/plugins/speculation-rules/helper.php
@@ -19,7 +19,7 @@
  *
  * @since 1.0.0
  *
- * @return array<string, mixed> Associative array of speculation rules by type.
+ * @return array<string, array<int, array<string, mixed>>> Associative array of speculation rules by type.
  */
 function plsr_get_speculation_rules(): array {
 	$option = get_option( 'plsr_speculation_rules' );
@@ -34,7 +34,7 @@ function plsr_get_speculation_rules(): array {
 		$option = array_merge( plsr_get_setting_default(), $option );
 	}
 
-	$mode      = $option['mode'];
+	$mode      = (string) $option['mode'];
 	$eagerness = $option['eagerness'];
 
 	$prefixer = new PLSR_URL_Pattern_Prefixer();
diff --git a/plugins/speculation-rules/hooks.php b/plugins/speculation-rules/hooks.php
index d9f201690a..b5731232cc 100644
--- a/plugins/speculation-rules/hooks.php
+++ b/plugins/speculation-rules/hooks.php
@@ -27,8 +27,8 @@ function plsr_print_speculation_rules(): void {
 	// This workaround is needed for WP 6.4. See <https://core.trac.wordpress.org/ticket/60320>.
 	$needs_html5_workaround = (
 		! current_theme_supports( 'html5', 'script' ) &&
-		version_compare( strtok( get_bloginfo( 'version' ), '-' ), '6.4', '>=' ) &&
-		version_compare( strtok( get_bloginfo( 'version' ), '-' ), '6.5', '<' )
+		version_compare( (string) strtok( (string) get_bloginfo( 'version' ), '-' ), '6.4', '>=' ) &&
+		version_compare( (string) strtok( (string) get_bloginfo( 'version' ), '-' ), '6.5', '<' )
 	);
 	if ( $needs_html5_workaround ) {
 		$backup_wp_theme_features = $GLOBALS['_wp_theme_features'];
@@ -36,7 +36,7 @@ function plsr_print_speculation_rules(): void {
 	}
 
 	wp_print_inline_script_tag(
-		wp_json_encode( $rules ),
+		(string) wp_json_encode( $rules ),
 		array( 'type' => 'speculationrules' )
 	);
 
diff --git a/plugins/speculation-rules/settings.php b/plugins/speculation-rules/settings.php
index 918b676c61..ae0c6ae818 100644
--- a/plugins/speculation-rules/settings.php
+++ b/plugins/speculation-rules/settings.php
@@ -206,8 +206,12 @@ function plsr_render_settings_field( array $args ): void {
 		return;
 	}
 
-	$value   = $option[ $args['field'] ];
-	$choices = call_user_func( "plsr_get_{$args['field']}_labels" );
+	$value    = $option[ $args['field'] ];
+	$callback = "plsr_get_{$args['field']}_labels";
+	if ( ! is_callable( $callback ) ) {
+		return;
+	}
+	$choices = call_user_func( $callback );
 
 	?>
 	<fieldset>
diff --git a/plugins/webp-uploads/helper.php b/plugins/webp-uploads/helper.php
index 8bc47dfea0..ccb5d3460f 100644
--- a/plugins/webp-uploads/helper.php
+++ b/plugins/webp-uploads/helper.php
@@ -106,21 +106,22 @@ function webp_uploads_generate_additional_image_source( int $attachment_id, stri
 	if ( is_wp_error( $image ) ) {
 		return $image;
 	}
+	if ( is_array( $image ) && array_key_exists( 'file', $image ) && is_string( $image['file'] ) ) {
+		// The filtered image provided all we need to short-circuit here.
+		if ( array_key_exists( 'filesize', $image ) && is_int( $image['filesize'] ) && $image['filesize'] > 0 ) {
+			return $image;
+		}
 
-	if (
-		is_array( $image ) &&
-		! empty( $image['file'] ) &&
-		(
-			! empty( $image['path'] ) ||
-			array_key_exists( 'filesize', $image )
-		)
-	) {
-		return array(
-			'file'     => $image['file'],
-			'filesize' => array_key_exists( 'filesize', $image )
-				? $image['filesize']
-				: wp_filesize( $image['path'] ),
-		);
+		// Supply the filesize based on the filter-provided path.
+		if ( array_key_exists( 'path', $image ) && is_int( $image['path'] ) ) {
+			$filesize = wp_filesize( $image['path'] );
+			if ( $filesize > 0 ) {
+				return array(
+					'file'     => $image['file'],
+					'filesize' => $filesize,
+				);
+			}
+		}
 	}
 
 	$allowed_mimes = array_flip( wp_get_mime_types() );
@@ -133,7 +134,7 @@ function webp_uploads_generate_additional_image_source( int $attachment_id, stri
 	}
 
 	$image_path = wp_get_original_image_path( $attachment_id );
-	if ( ! file_exists( $image_path ) ) {
+	if ( ! $image_path || ! file_exists( $image_path ) ) {
 		return new WP_Error( 'original_image_file_not_found', __( 'The original image file does not exists, subsizes are created out of the original image.', 'webp-uploads' ) );
 	}
 
diff --git a/plugins/webp-uploads/hooks.php b/plugins/webp-uploads/hooks.php
index b37ec51654..2266eff793 100644
--- a/plugins/webp-uploads/hooks.php
+++ b/plugins/webp-uploads/hooks.php
@@ -26,12 +26,22 @@
  * @see   wp_generate_attachment_metadata()
  * @see   webp_uploads_get_upload_image_mime_transforms()
  *
+ * @phpstan-param array{
+ *      width: int,
+ *      height: int,
+ *      file: string,
+ *      sizes: array<string, array{ file: string, width: int, height: int, 'mime-type': string }>,
+ *      image_meta: array<string, mixed>,
+ *      filesize: int
+ *  } $metadata
+ *
  * @param array<string, mixed> $metadata      An array with the metadata from this attachment.
  * @param int                  $attachment_id The ID of the attachment where the hook was dispatched.
+ *
  * @return array{
  *     width: int,
  *     height: int,
- *     file: non-falsy-string,
+ *     file: string,
  *     sizes: array<string, array{ file: string, width: int, height: int, 'mime-type': string, sources?: array<string, array{ file: string, filesize: int }> }>,
  *     image_meta: array<string, mixed>,
  *     filesize: int,
@@ -47,13 +57,13 @@ function webp_uploads_create_sources_property( array $metadata, int $attachment_
 
 	// Not a supported mime type to create the sources property.
 	$mime_type = get_post_mime_type( $attachment_id );
-	if ( ! isset( $valid_mime_transforms[ $mime_type ] ) ) {
+	if ( ! is_string( $mime_type ) || ! isset( $valid_mime_transforms[ $mime_type ] ) ) {
 		return $metadata;
 	}
 
 	$file = get_attached_file( $attachment_id, true );
 	// File does not exist.
-	if ( ! file_exists( $file ) ) {
+	if ( ! $file || ! file_exists( $file ) ) {
 		return $metadata;
 	}
 
@@ -116,7 +126,9 @@ function webp_uploads_create_sources_property( array $metadata, int $attachment_
 	if (
 		! in_array( $mime_type, $valid_mime_transforms[ $mime_type ], true ) &&
 		isset( $valid_mime_transforms[ $mime_type ][0] ) &&
-		isset( $allowed_mimes[ $mime_type ] )
+		isset( $allowed_mimes[ $mime_type ] ) &&
+		array_key_exists( 'file', $metadata ) &&
+		is_string( $metadata['file'] )
 	) {
 		$valid_mime_type = $valid_mime_transforms[ $mime_type ][0];
 
@@ -134,12 +146,17 @@ function webp_uploads_create_sources_property( array $metadata, int $attachment_
 
 			// If WordPress already modified the original itself, keep the original and discard WordPress's generated version.
 			if ( ! empty( $metadata['original_image'] ) ) {
-				$uploadpath = wp_get_upload_dir();
-				wp_delete_file_from_directory( get_attached_file( $attachment_id ), $uploadpath['basedir'] );
+				$uploadpath    = wp_get_upload_dir();
+				$attached_file = get_attached_file( $attachment_id );
+				if ( $attached_file ) {
+					wp_delete_file_from_directory( $attached_file, $uploadpath['basedir'] );
+				}
 			}
 
 			// Replace the attached file with the custom MIME type version.
-			$metadata = _wp_image_meta_replace_original( $saved_data, $original_image, $metadata, $attachment_id );
+			if ( $original_image ) {
+				$metadata = _wp_image_meta_replace_original( $saved_data, $original_image, $metadata, $attachment_id );
+			}
 
 			// Unset sources entry for the original MIME type, then save (to avoid inconsistent data
 			// in case of an error after this logic).
@@ -233,6 +250,15 @@ function webp_uploads_create_sources_property( array $metadata, int $attachment_
  *
  * @see wp_get_missing_image_subsizes()
  *
+ * @phpstan-param array{
+ *     width: int,
+ *     height: int,
+ *     file: string,
+ *     sizes: array<string, array{file: string, width: int, height: int, mime-type: string}>,
+ *     image_meta: array<string, mixed>,
+ *     filesize: int
+ * } $image_meta
+ *
  * @param array|mixed          $missing_sizes Associative array of arrays of image sub-sizes.
  * @param array<string, mixed> $image_meta    The metadata from the image.
  * @param int                  $attachment_id The ID of the attachment.
@@ -716,7 +742,7 @@ function webp_uploads_wepb_fallback(): void {
 	$javascript = ob_get_clean();
 
 	wp_print_inline_script_tag(
-		preg_replace( '/\s+/', '', $javascript ),
+		preg_replace( '/\s+/', '', (string) $javascript ),
 		array(
 			'id'            => 'webpUploadsFallbackWebpImages',
 			'data-rest-api' => esc_url_raw( trailingslashit( get_rest_url() ) ),
diff --git a/plugins/webp-uploads/image-edit.php b/plugins/webp-uploads/image-edit.php
index 6a38323d98..4b7ef4e4c6 100644
--- a/plugins/webp-uploads/image-edit.php
+++ b/plugins/webp-uploads/image-edit.php
@@ -42,7 +42,7 @@
  *     image_meta: array<string, mixed>,
  *     filesize: int,
  *     original_image?: string,
- *     sources: array<string, array{ file: string, filesize: int }>
+ *     sources?: array<string, array{ file: string, filesize: int }>
  * } Metadata with sources added.
  */
 function webp_uploads_update_sources( array $metadata, array $valid_mime_transforms, array $main_images, array $subsized_images ): array {
@@ -194,7 +194,7 @@ static function ( $metadata, $post_meta_id ) use ( $post_id, $file_path, $mime_t
 					continue;
 				}
 
-				if ( ! $editor::supports_mime_type( $targeted_mime ) ) {
+				if ( $editor instanceof WP_Image_Editor && ! $editor::supports_mime_type( $targeted_mime ) ) {
 					continue;
 				}
 
@@ -228,7 +228,7 @@ static function ( $metadata, $post_meta_id ) use ( $post_id, $file_path, $mime_t
 					}
 
 					$subsized_images[ $targeted_mime ] = array( 'thumbnail' => $result );
-				} else {
+				} elseif ( $editor instanceof WP_Image_Editor ) {
 					$destination = trailingslashit( $original_directory ) . "{$filename}.{$extension}";
 
 					remove_filter( 'image_editor_output_format', 'webp_uploads_filter_image_editor_output_format', 10 );
@@ -263,6 +263,16 @@ static function ( $metadata, $post_meta_id ) use ( $post_id, $file_path, $mime_t
  *
  * @see wp_update_attachment_metadata()
  *
+ * @phpstan-param array{
+ *        width: int,
+ *        height: int,
+ *        file: string,
+ *        sizes: array<string, array{ file: string, width: int, height: int, 'mime-type': string, sources?: array<string, array{ file: string, filesize: int }> }>,
+ *        image_meta: array<string, mixed>,
+ *        filesize: int,
+ *        original_image: string
+ *    } $data
+ *
  * @param array<string, mixed> $data          The current metadata of the attachment.
  * @param int                  $attachment_id The ID of the current attachment.
  *
@@ -305,8 +315,20 @@ function webp_uploads_update_attachment_metadata( array $data, int $attachment_i
  *
  * @since 1.0.0
  *
+ * @phpstan-param array{
+ *       width: int,
+ *       height: int,
+ *       file: string,
+ *       sizes: array<string, array{ file: string, width: int, height: int, 'mime-type': string }>,
+ *       image_meta: array<string, mixed>,
+ *       filesize: int,
+ *       original_image: string,
+ *       sources?: array<string, array{ file: string, filesize: int }>
+ *   } $data
+ *
  * @param int                  $attachment_id The ID representing the attachment.
  * @param array<string, mixed> $data          The current metadata of the attachment.
+ *
  * @return array{
  *     width: int,
  *     height: int,
@@ -437,6 +459,16 @@ function webp_uploads_get_next_full_size_key_from_backup( int $attachment_id ):
  *
  * @since 1.0.0
  *
+ * @phpstan-param array{
+ *        width: int,
+ *        height: int,
+ *        file: string,
+ *        sizes: array<string, array{ file: string, width: int, height: int, 'mime-type': string }>,
+ *        image_meta: array<string, mixed>,
+ *        filesize: int,
+ *        original_image: string
+ *    } $data
+ *
  * @param int                  $attachment_id The ID of the attachment.
  * @param array<string, mixed> $data          The current metadata to be stored in the attachment.
  * @return array{
@@ -446,7 +478,7 @@ function webp_uploads_get_next_full_size_key_from_backup( int $attachment_id ):
  *     sizes: array<string, array{ file: string, width: int, height: int, 'mime-type': string }>,
  *     image_meta: array<string, mixed>,
  *     filesize: int,
- *     sources: array<string, array{ file: string, filesize: int }>,
+ *     sources?: array<string, array{ file: string, filesize: int }>,
  *     original_image: string
  * } The updated metadata of the attachment.
  */
diff --git a/plugins/webp-uploads/rest-api.php b/plugins/webp-uploads/rest-api.php
index 947652f947..ab04bc732e 100644
--- a/plugins/webp-uploads/rest-api.php
+++ b/plugins/webp-uploads/rest-api.php
@@ -49,6 +49,6 @@ function webp_uploads_update_rest_attachment( WP_REST_Response $response, WP_Pos
 		unset( $data['media_details']['sources'] );
 	}
 
-	return rest_ensure_response( $data );
+	return new WP_REST_Response( $data );
 }
 add_filter( 'rest_prepare_attachment', 'webp_uploads_update_rest_attachment', 10, 2 );
diff --git a/tests/includes/server-timing/perflab-server-timing-tests.php b/tests/includes/server-timing/perflab-server-timing-tests.php
index 4c93f7e754..9c6df67514 100644
--- a/tests/includes/server-timing/perflab-server-timing-tests.php
+++ b/tests/includes/server-timing/perflab-server-timing-tests.php
@@ -44,7 +44,8 @@ public function test_register_metric_stores_metrics_and_runs_measure_callback():
 		$this->server_timing->register_metric(
 			'test-metric',
 			array(
-				'measure_callback' => static function () use ( &$called ): void {
+				'measure_callback' => static function ( Perflab_Server_Timing_Metric $metric ) use ( &$called ): void {
+					unset( $metric );
 					$called = true;
 				},
 				'access_cap'       => 'exist',
@@ -61,7 +62,8 @@ public function test_register_metric_runs_measure_callback_based_on_access_cap()
 		$this->server_timing->register_metric(
 			'test-metric',
 			array(
-				'measure_callback' => static function () use ( &$called ): void {
+				'measure_callback' => static function ( Perflab_Server_Timing_Metric $metric ) use ( &$called ): void {
+					unset( $metric );
 					$called = true;
 				},
 				'access_cap'       => $access_cap,
@@ -75,7 +77,8 @@ public function test_register_metric_runs_measure_callback_based_on_access_cap()
 		$this->server_timing->register_metric(
 			'test-metric-2',
 			array(
-				'measure_callback' => static function () use ( &$called ): void {
+				'measure_callback' => static function ( Perflab_Server_Timing_Metric $metric ) use ( &$called ): void {
+					unset( $metric );
 					$called = true;
 				},
 				'access_cap'       => $access_cap,
@@ -141,7 +144,7 @@ public function test_register_metric_replaces_slashes(): void {
 		$this->server_timing->register_metric(
 			'foo/bar/baz',
 			array(
-				'measure_callback' => static function ( $metric ): void {
+				'measure_callback' => static function ( Perflab_Server_Timing_Metric $metric ): void {
 					$metric->set_value( 123 );
 				},
 				'access_cap'       => 'exist',
@@ -166,13 +169,13 @@ public function test_get_header( string $expected, array $metrics ): void {
 	 * @return array<string, mixed>
 	 */
 	public function data_get_header(): array {
-		$measure_42         = static function ( $metric ): void {
+		$measure_42         = static function ( Perflab_Server_Timing_Metric $metric ): void {
 			$metric->set_value( 42 );
 		};
-		$measure_300        = static function ( $metric ): void {
+		$measure_300        = static function ( Perflab_Server_Timing_Metric $metric ): void {
 			$metric->set_value( 300 );
 		};
-		$measure_12point345 = static function ( $metric ): void {
+		$measure_12point345 = static function ( Perflab_Server_Timing_Metric $metric ): void {
 			$metric->set_value( 12.345 );
 		};
 
diff --git a/tests/plugins/optimization-detective/class-od-url-metrics-group-collection-tests.php b/tests/plugins/optimization-detective/class-od-url-metrics-group-collection-tests.php
index 8369c7b521..bdd9fea693 100644
--- a/tests/plugins/optimization-detective/class-od-url-metrics-group-collection-tests.php
+++ b/tests/plugins/optimization-detective/class-od-url-metrics-group-collection-tests.php
@@ -52,7 +52,7 @@ public function data_provider_test_construction(): array {
 				'breakpoints'   => array( 'narrow' ),
 				'sample_size'   => 3,
 				'freshness_ttl' => HOUR_IN_SECONDS,
-				'exception'     => PHP_MAJOR_VERSION >= 8 ? TypeError::class : InvalidArgumentException::class,
+				'exception'     => InvalidArgumentException::class,
 			),
 			'negative_sample_size_bad'   => array(
 				'url_metrics'   => array(),
diff --git a/tests/plugins/optimization-detective/optimization-tests.php b/tests/plugins/optimization-detective/optimization-tests.php
index 7c8eddfa83..659a33bae4 100644
--- a/tests/plugins/optimization-detective/optimization-tests.php
+++ b/tests/plugins/optimization-detective/optimization-tests.php
@@ -27,7 +27,7 @@ class OD_Optimization_Tests extends WP_UnitTestCase {
 	public function set_up(): void {
 		$this->original_request_uri    = $_SERVER['REQUEST_URI'];
 		$this->original_request_method = $_SERVER['REQUEST_METHOD'];
-		$this->default_mimetype        = ini_get( 'default_mimetype' );
+		$this->default_mimetype        = (string) ini_get( 'default_mimetype' );
 		parent::set_up();
 	}
 
diff --git a/tests/plugins/webp-uploads/helper-tests.php b/tests/plugins/webp-uploads/helper-tests.php
index a30971c397..aa3aa488f2 100644
--- a/tests/plugins/webp-uploads/helper-tests.php
+++ b/tests/plugins/webp-uploads/helper-tests.php
@@ -277,8 +277,8 @@ public function it_should_create_an_image_with_filter_webp_uploads_pre_generate_
 			'webp_uploads_pre_generate_additional_image_source',
 			static function () {
 				return array(
-					'file' => 'image.webp',
-					'path' => '/tmp/image.webp',
+					'file'     => 'image.webp',
+					'filesize' => 1024,
 				);
 			}
 		);