For filehosts probably at least 90% of all uploads are illegal if you ask a copyright lawyer. 🥴 But that’s mostly just people sharing culture.

Of course damn CSAM is a different (and actual) kind of issue and plain awful to deal with. If I remember correctly some organisation from the US provides a free list of checksums of known crap that’s circulating to automatically check media file signatures against, I think that’s the first thing I’d look for to have some baseline defense against those disgusting fucks. Or (depending on your jurisdiction) even be compatible with the law for public hosting services.

Better use Tor & a trustworthy search engine when looking for infos how to implement such an upload filter, I wouldn’t trust automated systems from Google to not misinterpret your intention with these topics.