Try with WaitForPendingFinalizers

build/ReactiveUI.props

@@ -1,5 +1,5 @@
 <Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <ItemGroup>
-    <PackageReference Include="ReactiveUI" Version="9.0.1" />
+    <PackageReference Include="ReactiveUI" Version="10.2.2" />
   </ItemGroup>
 </Project>

src/Avalonia.ReactiveUI/AvaloniaActivationForViewFetcher.cs

@@ -27,7 +27,7 @@ namespace Avalonia.ReactiveUI
         /// <summary>
         /// Returns activation observable for activatable Avalonia view.
         /// </summary>
-        public IObservable<bool> GetActivationForView(IActivatable view)
+        public IObservable<bool> GetActivationForView(IActivatableView view)
         {
             if (!(view is IVisual visual)) return Observable.Return(false);
             if (view is WindowBase window) return GetActivationForWindowBase(window);

src/Avalonia.ReactiveUI/RoutedViewHost.cs

@@ -53,7 +53,7 @@ namespace Avalonia.ReactiveUI
     /// ReactiveUI routing documentation website</see> for more info.
     /// </para>
     /// </remarks>
-    public class RoutedViewHost : TransitioningContentControl, IActivatable, IEnableLogger
+    public class RoutedViewHost : TransitioningContentControl, IActivatableView, IEnableLogger
     {
         /// <summary>
         /// <see cref="AvaloniaProperty"/> for the <see cref="Router"/> property.

tests/Avalonia.Markup.UnitTests/Parsers/ExpressionObserverBuilderTests_AttachedProperty.cs

@@ -120,6 +120,8 @@ namespace Avalonia.Markup.UnitTests.Parsers
             var result = run();
             result.Item1.Subscribe(x => { });
 
+            GC.Collect();
+            GC.WaitForPendingFinalizers();
             GC.Collect();
 
             Assert.Null(result.Item2.Target);

tests/Avalonia.ReactiveUI.UnitTests/AvaloniaActivationForViewFetcherTest.cs

@@ -20,9 +20,9 @@ namespace Avalonia.ReactiveUI.UnitTests
 {
     public class AvaloniaActivationForViewFetcherTest
     {
-        public class TestUserControl : UserControl, IActivatable { }
+        public class TestUserControl : UserControl, IActivatableView { }
 
-        public class TestUserControlWithWhenActivated : UserControl, IActivatable
+        public class TestUserControlWithWhenActivated : UserControl, IActivatableView
         {
             public bool Active { get; private set; }
 
@@ -38,7 +38,7 @@ namespace Avalonia.ReactiveUI.UnitTests
             }
         }
 
-        public class TestWindowWithWhenActivated : Window, IActivatable
+        public class TestWindowWithWhenActivated : Window, IActivatableView
         {
             public bool Active { get; private set; }
 
@@ -54,7 +54,7 @@ namespace Avalonia.ReactiveUI.UnitTests
             }
         }
 
-        public class ActivatableViewModel : ISupportsActivation
+        public class ActivatableViewModel : IActivatableViewModel
         {
             public ViewModelActivator Activator { get; }