Fixed the iOS BackButton title does not update when set to an empty string or whitespace

src/Controls/src/Core/Compatibility/Handlers/Shell/iOS/ShellPageRendererTracker.cs

@@ -400,7 +400,7 @@ void UpdateBackButtonTitle()
 					var previousNavItem = viewControllers[count - 2].NavigationItem;
 					if (previousNavItem != null)
 					{
-						if (!String.IsNullOrWhiteSpace(text))
+						if (text is not null)
 						{
 							var barButtonItem = (previousNavItem.BackBarButtonItem ??= new UIBarButtonItem());
 							barButtonItem.Title = text;

src/Controls/tests/TestCases.HostApp/Issues/Issue25742.cs

@@ -0,0 +1,63 @@
+namespace Maui.Controls.Sample.Issues
+{
+	[Issue(IssueTracker.Github, 25742, "iOS BackButton title does not update when set to an empty string or whitespace", PlatformAffected.iOS)]
+	public class Issue25742 : Shell
+	{
+		public Issue25742()
+		{
+			 // Register the routes
+            Routing.RegisterRoute("page2", typeof(Issue25742Page2));
+
+            // Create and add Shell contents
+            var page1 = new ShellContent
+            {
+                Title = "Page 1",
+                Content = new Issue25742Page1()
+            };
+
+            Items.Add(page1);
+		}
+	}
+
+    public class Issue25742Page1 : ContentPage
+    {
+        public Issue25742Page1()
+        {
+            Title = "Page 1";
+            var navigateButton = new Button
+            {
+                Text = "Go to Page 2",
+				AutomationId = "GotoPage2"
+            };
+            navigateButton.Clicked += OnNavigateToPage2Clicked;
+
+            Content = new StackLayout
+            {
+                Children = { navigateButton }
+            };
+        }
+
+        private async void OnNavigateToPage2Clicked(object sender, EventArgs e)
+        {
+            await Shell.Current.GoToAsync("page2"); // Use the route name "page2" here
+        }
+    }
+
+	public class Issue25742Page2 : ContentPage
+    {
+        public Issue25742Page2()
+        {
+            Title = "Page 2";
+            Content = new StackLayout
+            {
+                Children = { new Label { Text = "Welcome to Page 2" } }
+            };
+
+            // Set back button behavior with empty TextOverride
+            Shell.SetBackButtonBehavior(this, new BackButtonBehavior
+            {
+                TextOverride = "" // Removes the back button text
+            });
+        }
+    }
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue27542.cs

@@ -0,0 +1,26 @@
+#if ANDROID || IOS
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues
+{
+	public class Issue25742 : _IssuesUITest
+	{
+		public override string Issue => "iOS BackButton title does not update when set to an empty string or whitespace";
+
+		public Issue25742(TestDevice device) : base(device)
+		{
+		}
+
+		[Test]
+		[Category(UITestCategories.Shell)]
+		public void UpdatedBackButtonTitleForEmptyString()
+		{
+			App.WaitForElement("GotoPage2");
+			App.Tap("GotoPage2");
+			VerifyScreenshot();	
+		}
+	}
+}
+#endif