Thank you. Like you I used Linux and still use Gimp. I've dabbled a bit in Krita and maybe tried MyPaint once or twice. You should have a look at Blender too if you're into 3D art.

I'm a 2D artist but I looked into doing Non-Photorealistic Rendering (NPR) in Blender. I just can't understand Blender's user interface.

Yeah that's a common gripe people have with Blender. I was lucky to learn it at a time when I didn't have any prior experience with other 3D software so I wasn't put off by the weird UI.