IANAL, but from what I understand, you can put anything you want in a contract, but it doesn't mean it's enforceable.

So the reason why companies put in non-compete clauses is mostly because people believe it, not because it's really enforceable.

Now if former twitter employees were still getting severance from Twitter while working at Meta, that could be an issue. But generally speaking, if you're not getting money (consideration) non-compete clauses don't matter much.

Noncompetes are basically unenforceable in California, you can make people sign them but they’re about as useful as if they were made out of toilet paper

I think that it is also different if you get fired. Don’t know in detail, but I assume that if they fire you without a valid cause they don’t have any grounds to complain that you did a sensitive and unique work.