fix: Adjust IsFocusable on Popup

src/Uno.UI/UI/Xaml/Controls/Popup/Popup.Base.cs

@@ -111,6 +111,11 @@ partial void OnIsOpenChangedPartial(bool oldIsOpen, bool newIsOpen)
 					Focus(FocusState.Programmatic);
 				}
 			}
+
+			if (IsLightDismissEnabled || IsForFlyout)
+			{
+				m_fIsLightDismiss = true;
+			}
 		}
 		else
 		{
@@ -123,6 +128,8 @@ partial void OnIsOpenChangedPartial(bool oldIsOpen, bool newIsOpen)
 					_lastFocusedElement = null;
 				}
 			}
+
+			m_fIsLightDismiss = false;
 		}
 	}
 

src/Uno.UI/UI/Xaml/Controls/Popup/Popup.cs

@@ -351,7 +351,4 @@ internal Brush LightDismissOverlayBackground
 
 	internal static DependencyProperty LightDismissOverlayBackgroundProperty { get; } =
 		DependencyProperty.Register(nameof(LightDismissOverlayBackground), typeof(Brush), typeof(Popup), new FrameworkPropertyMetadata(defaultValue: null, propertyChangedCallback: (o, e) => ((Popup)o).ApplyLightDismissOverlayMode()));
-
-	// On WinUi, a popup is not IsTabStop but is somehow focusable. This is a workaround to match that behaviour.
-	internal override bool IsFocusableForFocusEngagement() => true;
 }

src/Uno.UI/UI/Xaml/Controls/Popup/Popup.h.mux.cs

@@ -0,0 +1,18 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Microsoft.UI.Xaml.Controls.Primitives;
+
+public partial class Popup
+{
+	private bool m_fIsLightDismiss;
+
+	internal override bool IsFocusable =>
+		m_fIsLightDismiss &&
+		IsVisible() &&
+		IsEnabledInternal() &&
+		AreAllAncestorsVisible();
+}