If it's legal it's free speech
That definition has a loophole so wide you could drive the Titanic through it.
"Sure, we're banning people from kneeling during the National Anthem, but that's not a restriction on free speech because it'll be illegal and thus not free speech once it's banned!"
I'd like to suggest instead that we go battle my 23 year old self (roughly half my age) who used to fetishize free speech in the same way most people do here. There's a world of difference between illegal, bad, and "Stuff you should feel obliged to republish." We can argue that legal bans and moderation within large communities are two different ways someone can restrict free speech, but that doesn't make the latter bad, merely something people should be wary of doing too broadly.
Google, Facebook, et al, should be thinking in terms of whether certain content actually harms society as a whole, and determining at what level to support that content. If, for example, someone is buying ads to harm a political candidate, the truth of those ads absolutely should be a factor before either decide to sell to the advertiser.
That's what they should be doing anyway. But I'd be extremely wary of any laws that force them to do so, beyond those that exist today that they allegedly have been ignoring or otherwise not enforcing properly.