I believe Krita is on F-Droid and it's my go-to program on desktop, tho I couldn't get ot to work correctly on my phone or the outdated tablets I could get my hands on (it launched, but I was stuck on a part of the screen and couldn't move, or close the window that opens at the start to create a document because the "close" button was outside my screen). so I don't know how it'll be on your tablet.
That aside, I really didn't find many open source Android apps for Graphic design. I sometimes use Pocket Paint, but it sucks and I only use it to make comically bad art for memes.