MapControl: Cannot add MapElements about microsoft-ui-xaml HOT 1 OPEN

I was now able to at least find a way to add some useless marker on the map (getting used to this control isn't straight-forward, also because it is missing documentation - or I am just unable to find it).

var mapIcon = new Microsoft.UI.Xaml.Controls.MapIcon();
var pos = new Windows.Devices.Geolocation.BasicGeoposition { Latitude = 20, Longitude = 20 };
mapIcon.Location = new Windows.Devices.Geolocation.Geopoint(pos);
elem_layer.MapElements.Add(mapIcon);

But I still don't see how I could do any customization of that marker (give it a custom thumbnail or at least a title). I also don't see to add polylines or shapes

from microsoft-ui-xaml.