This code works and is based on the only method available:
B4X:
Sub gmap_Click (Point As LatLng)
Dim xy() As Double = LatLonToXY(Point)
Log($"x = $1.2{xy(0)}, y = $1.2{xy(1))}"$
End Sub
Public Sub LatLonToXY(ll As LatLng) As Double()
Dim jo As JavaObject = gmap
jo = jo.GetFieldJO("map").RunMethod("getProjection", Null)
If jo = Null Then Return Array As Double(-1, -1)
jo = jo.RunMethod("fromLatLngToPoint", Array(ll))
Return Array As Double(jo.RunMethod("getX", Null), jo.RunMethod("getY", Null))
End Sub
I'm not sure how these values refer to the screen.