[Windows] Fixed the ContentView clip is not updated when wrapping inside the Border

src/Controls/tests/TestCases.HostApp/Issues/Issue30404.cs

@@ -0,0 +1,52 @@
+using Microsoft.Maui.Controls.Shapes;
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 30404, "[Windows] ContentView clip is not updated when wrapping inside the Border", PlatformAffected.UWP)]
+public class Issue30404 : ContentPage
+{
+    public Issue30404()
+    {
+        var border = new Border
+        {
+            HeightRequest = 200,
+            BackgroundColor = Colors.Green,
+            HorizontalOptions = LayoutOptions.Center,
+            VerticalOptions = LayoutOptions.Center
+        };
+
+        var customView = new Issue30404CustomContentView
+        {
+            HeightRequest = 100,
+            WidthRequest = 100,
+        };
+
+        border.Content = customView;
+        Content = border;
+    }
+}
+
+public class Issue30404CustomContentView : ContentView
+{
+    public Issue30404CustomContentView()
+    {
+        BackgroundColor = Colors.Red;
+        Content = new Label
+        {
+            Text = "Clipped Content",
+            TextColor = Colors.Blue,
+            AutomationId = "BorderContentLabel",
+            HorizontalOptions = LayoutOptions.Center,
+            VerticalOptions = LayoutOptions.Center
+        };
+
+        SizeChanged += OnSizeChanged;
+    }
+
+    private void OnSizeChanged(object sender, EventArgs e)
+    {
+        if (Width > 0 && Height > 0)
+        {
+            Clip = new RoundRectangleGeometry(25, new Rect(0, 0, Width, Height));
+        }
+    }
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue30404.cs

@@ -0,0 +1,22 @@
+#if TEST_FAILS_ON_IOS && TEST_FAILS_ON_CATALYST // Content of the border disappears when apply clip to it see https://github.com/dotnet/maui/issues/14164
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue30404 : _IssuesUITest
+{
+	public Issue30404(TestDevice device) : base(device) { }
+
+	public override string Issue => "[Windows] ContentView clip is not updated when wrapping inside the Border";
+
+	[Test]
+	[Category(UITestCategories.Border)]
+	public void ClipShouldApplyProperlyToTheContentOfBorder()
+	{
+		App.WaitForElement("BorderContentLabel");
+		VerifyScreenshot();
+	}
+}
+#endif

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

@@ -182,6 +182,13 @@ void UpdateClip(IShape? borderShape, double width, double height)
 			}
 
 			var visual = ElementCompositionPreview.GetElementVisual(Content);
+
+			// Prevent clip collision: When ContentView is inside Border, let WrapperView handle 
+			// clipping to avoid Border overwriting ContentView's clip geometry during SizeChanged.
+			if (visual.Clip != null && Content.Parent is WrapperView)
+			{
+				return;
+			}
 			var compositor = visual.Compositor;
 
 			PathF? clipPath;