It may be a bug of Android: Newer Android versions have further locker down sd card access. The implementation is apparently super slow for stuff like what Osmand uses. Dont put the map data onto the sd card or use one of the predefined locations

https://github.com/osmandapp/OsmAnd/issues/12046 https://github.com/osmandapp/OsmAnd/issues/13254

Edit: If that is not the culprit then check if OpenGL rendering is activated.

You can also deactivate unneeded features from being rendered (buildings, areas, etc). And lastly there are smaller road-only maps (no POI data and no adresses though)