Well... it's the law, and yet the lines aren't quite where we expect them to be.
Have you ever seen an informercial or something talking about a drug to fix something, and then it says something like "this drug has not been proven effective for this use"? That's pushing the line but not crossing it. Those people don't get arrested.
But if you said "Ivermectin is safe and effective for treating Covid", then you've probably crossed it. If you're making money from it, then you may have worse problems than Youtube banning your videos.
I don't know what Bret Weinstein says. If he says "this looks like it may work", he's probably OK. If he says "it's been shown to work", I would be surprised that the FDA hasn't done something.
[Edit: If he says "it's been shown to work" and he's selling it, that's where the FDA will almost certainly step in. If he says it but isn't himself selling it... I don't know how they respond to that.]
Disclaimer: IANAL.