I am by no means a master at OBS, and I wouldn’t know where to point you to learn. Everything I know I’ve learned by either poking around in the software or googling specific questions, i.e. “how to overlay twitch chat in OBS”. As you can probably guess, I used to use it to stream to twitch. Not very suddenly, mind, but I did it. Lol!
OBS is designed for streaming out and recording video, not really for music production. I’m sure there are some FOSS music production softwares worth checking out, though!
Listen, I love GIMP. I would never try to argue that the UI/UX is better than alternatives. There’s a reason it’s not the defacto tool to use in its industry, and it’s not the name.
That said, if you take the time to learn GIMP, it’s delightful. I personally like using GIMP more than, say, Photoshop, but I also learned photo manipulation on GIMP, and didn’t touch Photoshop until well after. GIMP’s UX leaves a lot to be desired for a newcomer to the software.