Oh and good luck regarding your transition from windows to Ubuntu. I see that you had different issues for your first time, it can be though sometimes but keep going you will eventually get yourself confortable and understand new things on how it works. You will not regret it
I mostly use GIMP.
I am also enthusiast about the https://graphite.rs/ project which is working in browser (love it or hate it for that).
Krita is amazing for drawing but may be intimidating.
I like MyPaint that I use as a whiteboard. It is easy to use and convenient