Update Program.cs

Demo/Program.cs

@@ -10,6 +10,7 @@ namespace Demo
         // Initialization code. Don't use any Avalonia, third-party APIs or any
         // SynchronizationContext-reliant code before AppMain is called: things aren't initialized
         // yet and stuff might break.
+        [STAThread]
         public static void Main(string[] args) => BuildAvaloniaApp()
             .StartWithClassicDesktopLifetime(args);
 
@@ -20,4 +21,4 @@ namespace Demo
                 .LogToTrace()
                 .UseReactiveUI();
     }
-}
+}