Trying to Bind command WinUI But Error

    private ICommand _buttonClickedCommand;

    public ICommand Button_ClickedCommand
    {
        get
        {
            if (_buttonClickedCommand == null)
            {
                _buttonClickedCommand = new RelayCommand(
                    param => startPage()
                );
            }
            return _buttonClickedCommand;
        }
    }

    private void startPage()
    {
        var pathToFolder = "C:\\Program Files\\Internet Explorer\\iexplore.exe";

        Process.Start(Environment.GetEnvironmentVariable("WINDIR") + @"\explorer.exe", pathToFolder);
    }

    private ICommand _buttonClickedCommand;

    public ICommand Button_ClickedCommand
    {
        get
        {
            if (_buttonClickedCommand == null)
            {
                _buttonClickedCommand = new RelayCommand(
                    param => startPage()
                );
            }
            return _buttonClickedCommand;
        }
    }

    private void startPage()
    {
        var pathToFolder = "C:\\Program Files\\Internet Explorer\\iexplore.exe";

        Process.Start(Environment.GetEnvironmentVariable("WINDIR") + @"\explorer.exe", pathToFolder);
    }