OsmDroid is the library used for displaying the map.
It's old, very poorly documented, and the development has stalled. It's not the optimal choice, as it also does weird things with different screen densities.

MapLibre (bozzy will like the name) is the open source fork of MapBox, and it's been adopted recently by the TransportR app.
It could be useful to switch to it.

Link: https://github.com/maplibre/maplibre-native/blob/main/platform/android/README.md