Don't use gimp! It's a piece of shit of a software! There's so much better! You're suffering uselessly.
You can try krita for free, it's illustration oriented and widely appreciated.
Most artists I know work on clip studio paint, it's a one time buy (the first edition is, idk for 2.0 I think it has a subscription system) and a GREAT software for illustration too, with a shit ton of nice feature to make comics quickly. A staple.
Paint Tool Sai is also an old classic. Also a one time buy iirc.
For photo edition and drawing, as a replacement for Photoshop, you have affinity designer which is completely free! You just need a Canva account (free too) I guess they got a partnership. Affinity burst in the room like the fucking kool aid man and yelled "YO BITCHES WE'RE REPLACING PHOTOSHOP" and from my surface use and a lot of feedback, they do! They're basically a copy lol. The only thing that's locked behind a premium account is AI features and nobody wants that shit anyway.
You can even use a Photoshop equivalent for free online! It's called photopea, fully free, it supports all formats and stuff. I used it when I was borrowing a pc when I was staying at my uncle's to tweak and clean my ink doodles.
I learned and used a shit ton of softwares, from the adobe suite to maya, substance painter and designer, a bit of unity and unreal, and I love zbrush which is a wonder to work with but a nightmare to learn, and a lot of others I forget.
But gimp is garbaaaaaage. I remember teaching a friend how to draw digitally, and we started on gimp cause it's free. And I was slamming my head on my keyboard it was so counter intuitive to learn and use, and missing a lot of features. I wasn't teaching shit I was battling while she waited and laughed at me. Then I was like "WAIT krita it's free let's try it!" And the teaching went flawlessly from that point on. She still laughs at my trauma.
I hope you don't have an emotional attachment to gimp cause I really just spit on it lol, no hard feelings.
ALSO I'm in a toxic relationship with photoshop, because there's one or two simple features that I use a lot that I can't find on other softwares. I tried but well. I draw simple things as a hobby now, I don't want to do the mental effort to set up and get used to another software. Maybe affinity has those features tho, it's worth trying I guess...
Note that I never paid Photoshop lol, I'm still on the CS7 version with a keygen that makes a horrible music when you open it.
WAIT idk which one of these run on other OS, but they're more and more common on linux a d stuff.