Krita "lemon", from some unofficial "neon" project, of Ubuntu, but running on Debian testing/Sid/Stretch.
I know it goes against all sorts of recommendations from both Debian and Ubuntu, perhaps even computing in general, but it seems to work fine so far.
The official version was quite slow to start up (to the point that sometimes I thought it simply wasn't going to ever start). And maybe it's just a difference between the versions (2.8 vs 2.9),...