<VerticalStackLayout>
     <Button x:Name="tapButton" Text="Tap button">
         <Button.GestureRecognizers>
             <TapGestureRecognizer Tapped="OnTapped" />
         </Button.GestureRecognizers>
     </Button>
     
     <Button Text="Add new Gesture" x:Name="addGestureButton" />
 </VerticalStackLayout>

public partial class MainPage : ContentPage
{
    public MainPage()
    {
        InitializeComponent();

        addGestureButton.Clicked += (s, e) =>
        {
            var p = new TapGestureRecognizer();
            p.Tapped += (s, e) =>
            {

            };
            tapButton.GestureRecognizers.Add(p);
        };
    }

    public void OnTapped(object sender, TappedEventArgs args)
    {
        // runs multiple times by one tap
    }
}