Hi! I'm not really an expert in game development or anything, but I think I might have come across something that could be relevant to what you're looking for. There's this online learning platform - I believe it's called ELVTR - that offers a course for 2D game artists. I stumbled upon it recently and saved the link:
https://uk.elvtr.com/course/2d-game-artist I don't know much about the course content or quality, to be honest, but it sounds like it might be along the lines of what you're after. Maybe you could check out their website? They should have all the details about the curriculum and what you can expect to learn. Sorry I can't be more helpful, but I hope this gives you a lead to explore!