我已为文件夹选取器引用此Folder Picker .NET MAUI链接。但我无法在文件夹选取器中指定特定的文件类型。
就像如果我指定类型为.txt，那么它应该只显示包含**.txt**文件的文件夹同样。

public async Task<string> PickFolder()
    {
        var folderPicker = new WindowsFolderPicker();
        // Might be needed to make it work on Windows 10
        folderPicker.FileTypeFilter.Add(".txt");

        // Get the current window's HWND by passing in the Window object
        var hwnd = ((MauiWinUIWindow)App.Current.Windows[0].Handler.PlatformView).WindowHandle;

        // Associate the HWND with the file picker
        WinRT.Interop.InitializeWithWindow.Initialize(folderPicker, hwnd);

        var result = await folderPicker.PickSingleFolderAsync();

        return result?.Path;
    }