c#
   public async void PickFolderButton_Click(object sender, RoutedEventArgs e)
   {
       // Clear previous returned file name, if it exists, between iterations of this scenario
       PickFolderOutputTextBlock.Text = "";

       // Create a folder picker
       FolderPicker openPicker = new Windows.Storage.Pickers.FolderPicker();

       // See the sample code below for how to make the window accessible from the App class.
       var window = App.CurrentWindow;

       // Retrieve the window handle (HWND) of the current WinUI 3 window.
       var hWnd = WinRT.Interop.WindowNative.GetWindowHandle(window);

       // Initialize the folder picker with the window handle (HWND).
       WinRT.Interop.InitializeWithWindow.Initialize(openPicker, hWnd);

       // Set options for your folder picker
       openPicker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary;
       openPicker.FileTypeFilter.Add("*");

       // Open the picker for the user to pick a folder
       StorageFolder folder = await openPicker.PickSingleFolderAsync();
       if (folder != null)
       {
           PickFolderOutputTextBlock.Text = folder.Path + @"\suyu";
       }
       else
       {
           PickFolderOutputTextBlock.Text = "No folder selected.";
       }
   }

c#
   public async void PickFolderButton_Click(object sender, RoutedEventArgs e)
   {
       // Clear previous returned file name, if it exists, between iterations of this scenario
       PickFolderOutputTextBlock.Text = "";

       // Create a folder picker
       FolderPicker openPicker = new Windows.Storage.Pickers.FolderPicker();

       // See the sample code below for how to make the window accessible from the App class.
       var window = App.CurrentWindow;

       // Retrieve the window handle (HWND) of the current WinUI 3 window.
       var hWnd = WinRT.Interop.WindowNative.GetWindowHandle(window);

       // Initialize the folder picker with the window handle (HWND).
       WinRT.Interop.InitializeWithWindow.Initialize(openPicker, hWnd);

       // Set options for your folder picker
       openPicker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary;
       openPicker.FileTypeFilter.Add("*");

       // Open the picker for the user to pick a folder
       StorageFolder folder = await openPicker.PickSingleFolderAsync();
       if (folder != null)
       {
           PickFolderOutputTextBlock.Text = folder.Path + @"\suyu";
       }
       else
       {
           PickFolderOutputTextBlock.Text = "No folder selected.";
       }
   }