I think that if I paint with my own brush a mario artwork that isn’t to Nintendo’s standart, they have the legal power to take it down from wherever I upload
Yes, fanart is almost certainly copyright infringement unless the copyright holder grants a license. Many companies have an official license for non-commercial fanart and generally nobody cares about it but if someone really wanted to they could absolutely file takedown requests against all fanart of their work.
I’m really not in the know abput these things but I have seen free fangames taken down because they used copyrighted property even though the creators don’t receive a penny.
I’ll compare it with the recent takedown of the Switch emulator Yuzu. It’s my understanding they actively solicited donations and piracy, both of which could be seen as commercial activities. Which in a project of that scale the latter was their downfall, meanwhile Ryujinx is still up and running. But we’ll see if that remains true.