Last I used MAPSUI in an android application (xamarin), vector tiles were not supported. It seems they are now supported through a MbTilesTileSource. This can load a local mbtiles resource, but how can an online tile source like mapbox be used?
This is not something I see represented in the mapsui samples, and the documentation is somewhat lacking still, so I hope someone here might know.
Vector tiles are still not supported in v4. MbTiles can be used to load raster tiles but not vector.