Add code to show desired syntax.

samples/ControlCatalog/App.xaml

@@ -17,4 +17,9 @@
     </Style>
     <StyleInclude Source="/SideBar.xaml"/>
   </Application.Styles>
+  <NativeMenu.Menu>
+    <NativeMenu>
+      <NativeMenuItem Header="About ControlCatalog" Command="{Binding AboutCommand}" />
+    </NativeMenu>
+  </NativeMenu.Menu>
 </Application>

samples/ControlCatalog/App.xaml.cs

@@ -1,18 +1,32 @@
 using System;
+using System.Reactive;
 using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Markup.Xaml;
+using ReactiveUI;
 
 namespace ControlCatalog
 {
     public class App : Application
     {
+        public App()
+        {
+            DataContext = this;
+
+            AboutCommand = ReactiveCommand.Create(() =>
+            {
+
+            });
+        }
+
         public override void Initialize()
         {
             AvaloniaXamlLoader.Load(this);
         }
 
+        public ReactiveCommand<Unit, Unit> AboutCommand { get; }
+
         public override void OnFrameworkInitializationCompleted()
         {
             if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktopLifetime)