[Windows] Fix for setting IsClippedToBounds="True" inside a Border control will crash on Windows

src/Controls/tests/TestCases.HostApp/Issues/Issue18937.xaml

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage
+    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+    x:Class="Maui.Controls.Sample.Issues.Issue18937">
+
+  <Border>
+    <StackLayout BackgroundColor="red" 
+                 IsClippedToBounds="True">
+      <Label AutomationId="Label" 
+             Text="Label Inside the Border" 
+             VerticalOptions="Center"
+             HorizontalOptions="Center"/>
+    </StackLayout>
+  </Border>
+
+</ContentPage>

src/Controls/tests/TestCases.HostApp/Issues/Issue18937.xaml.cs

@@ -0,0 +1,12 @@
+namespace Maui.Controls.Sample.Issues
+{
+
+	[Issue(IssueTracker.Github, 18937, "[Windows] Setting IsClippedToBound is true inside a Border control will crash on Windows", PlatformAffected.UWP)]
+	public partial class Issue18937 : ContentPage
+	{
+		public Issue18937()
+		{
+			InitializeComponent();
+		}
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue18937.cs

@@ -0,0 +1,21 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues
+{
+	public class Issue18937 : _IssuesUITest
+	{
+		public Issue18937(TestDevice device) : base(device) { }
+
+		public override string Issue => "[Windows] Setting IsClippedToBound is true inside a Border control will crash on Windows";
+
+		[Test]
+		[Category(UITestCategories.Border)]
+		public void ExceptionShouldNotOccurWhenIsClippedToBoundsIsTrue()
+		{
+			var testLabel = App.WaitForElement("Label");
+			Assert.That(testLabel.GetText(), Is.EqualTo("Label Inside the Border"));
+		}
+	}
+}

src/Core/src/Platform/Windows/ContentPanel.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Numerics;
+using System.Threading.Tasks;
 using Microsoft.Graphics.Canvas;
 using Microsoft.Maui.Graphics;
 #if MAUI_GRAPHICS_WIN2D
@@ -162,7 +163,7 @@ void UpdateBorder(IShape? strokeShape)
 			UpdateClip(strokeShape, width, height);
 		}
 
-		void UpdateClip(IShape? borderShape, double width, double height)
+		async void UpdateClip(IShape? borderShape, double width, double height)
 		{
 			if (Content is null)
 			{
@@ -182,6 +183,12 @@ void UpdateClip(IShape? borderShape, double width, double height)
 			}
 
 			var visual = ElementCompositionPreview.GetElementVisual(Content);
+
+			visual.Clip = null;
+
+			//Adding Task.Yield ensures that all layouts are properly updated before applying the clip.
+			await Task.Yield();
+
 			var compositor = visual.Compositor;
 
 			PathF? clipPath;