Searching in f-droid for “paint” or “draw” gives this result: : F-Droid Search: paint and https://search.f-droid.org/?q=draw&lang=en
I use Pocket Paint | F-Droid - Free and Open Source Android App Repository because it has the most features.
For anotating screenshots i like Simple Draw Pro | F-Droid - Free and Open Source Android App Repository