I've been using krita for a while now to do pixel art on android, it works great, but you need to play with the setting to make it work properly.
Recently I found Drawpile, which is based on krita but optimized for android. https://f-droid.org/packages/net.drawpile/
There's someone looking for collaboration to fork Mull https://redlib.pussthecat.org/r/fossdroid/comments/1hlg8zx/seeking_collaborators_for_mull_browser_fork/