This will likely be covered under parody.
As dowie points out, memes will be impacted because YT (for example) will have to use an algorithm to check every single video and an algorithm can not decide what is parody or transformative use - like a meme - it can only say "there is copyrighted material here" so even though the EU says "memes aren't subject to Art 13", the companies algorithm will be the instrument that bans memes instead, which shows that dowie is correct, the "impact" of the law will have more effect than the law intends.
Will they be enforced to check every upload, or just comply to legitimate removal requests?
they dont as long as they ban/stop EU IP's from getting to their services. Similar thing with GDPR many US sites wont allow EU IP's in.Stupid question alert but why do social media companies based in the US have to comply with this at all?
Having seen the saga Martin Lewis has had getting fake ads taken down on Facebook and their frankly shocking attitude, I have no sympathy for the big platforms.
Google threatening to block small EU producers if the EU doesn't bow to their demands should be the real scandal.