those really are the main ways but a few other ways i can think of are adoptables (where you make a design and sell it) and commercial work! or of course, being lucky enough to find work in the art industry like animation/storyboarding etc.

there’s selling digital goods like digital doujinshis, custom photoshop brushes, adoptable bases etc. for example as well (gumroad is good for that) and of course selling merch, but that means you need money to make money… other than that, commissions and donations really are the main ways artists make their money i think? at least online :O

(if anyone knows more ways feel free to reply!!!!)