[OOBE]Fix msgMonitor to prevent window maximizing (#31136)

src/settings-ui/Settings.UI/SettingsXAML/OobeWindow.xaml.cs

@@ -20,7 +20,7 @@ namespace Microsoft.PowerToys.Settings.UI
     /// <summary>
     /// An empty window that can be used on its own or navigated to within a Frame.
     /// </summary>
-    public sealed partial class OobeWindow : WindowEx
+    public sealed partial class OobeWindow : WindowEx, IDisposable
     {
         private PowerToysModules initialModule;
 
@@ -31,6 +31,8 @@ namespace Microsoft.PowerToys.Settings.UI
         private WindowId _windowId;
         private IntPtr _hWnd;
         private AppWindow _appWindow;
+        private WindowMessageMonitor _msgMonitor;
+        private bool disposedValue;
 
         public OobeWindow(PowerToysModules initialModule)
         {
@@ -59,8 +61,8 @@ namespace Microsoft.PowerToys.Settings.UI
 
             this.initialModule = initialModule;
 
-            var msgMonitor = new WindowMessageMonitor(this);
-            msgMonitor.WindowMessageReceived += (_, e) =>
+            _msgMonitor = new WindowMessageMonitor(this);
+            _msgMonitor.WindowMessageReceived += (_, e) =>
             {
                 const int WM_NCLBUTTONDBLCLK = 0x00A3;
                 if (e.Message.MessageId == WM_NCLBUTTONDBLCLK)
@@ -132,5 +134,22 @@ namespace Microsoft.PowerToys.Settings.UI
                 mainWindow.CloseHiddenWindow();
             }
         }
+
+        private void Dispose(bool disposing)
+        {
+            if (!disposedValue)
+            {
+                _msgMonitor?.Dispose();
+
+                disposedValue = true;
+            }
+        }
+
+        public void Dispose()
+        {
+            // Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
+            Dispose(disposing: true);
+            GC.SuppressFinalize(this);
+        }
     }
 }