"Free Speech" in the American legal sense (1st Amendment to the Constitution) applies to government prohibition on speech, with a particular emphasis on political speech.

It doesn't prevent one person from prohibiting speech... I can tell a pastor to stop preaching on my lawn. But, the government cannot tell a pastor not to preach in the publicly-owned town square (generally, there are exceptions).

There are arguments that certain online forums are effectively "town squares in the internet age" (Twitter in particular, at least pre-Musk). But, I always found that analogy to fall apart - twitter (or whatever online forum) is more like an op-ed section in a newspaper, IMO. And newspapers don't have to publish every op-ed that gets submitted.

Also, the 1st Amendment does not protect you from the consequences of your speech. I can call my boss an asshole to his face legally - and he can fire me (generally, there are labor protections and exceptions).