I have been a user of OSMAND+ for years and I love it
I’ve been experiencing this problem recently: when I zoom on a map the map enlarges but doesn’t adjust the resolution, so the map instead of being more detailed are just grainy
Instead of OsmAnd’s locally rendered maps you seem to be using raster maps. These can only display at the resolution the external source supplies. For fully zoomable vector maps use the built in l cal rendering.