TIL about skeb. I rather commission for art of my OCs instead of fanart of existing characters, so IDK how that'd fly.
Personally, I skew towards commissioning art (for myself, I'd pay upwards to $$$s, because I like splurging on myself for quality art). If I was in a position to donate, I'd probably donate to scanlation groups (I genuinely appreciate the time that volunteers throw together for a noob like me) or commission a manga I bought that never finished serialization despite being licensed back in the 00s. Then, like the above, probably a doujinshi artist.
If an artist I liked was taking commissions, I'd throw all the money I'd have for something I want. That same spirit isn't around for the existing art they do. But at least I can leave a comment of thank you or a like somewhere (if they're on Webtoon) to show my support that way. Just honest opinion .