Earlier quoted context omitted.
I agree people are often confused by what the 1st Amendment guarantees, however government isn't the only threat to free speech, especially on the internet where large platforms yield more power than many smaller countries. I'm not saying private entities should be subject to the 1st Amendment, but we shouldn't give them a free pass to censor just because we happen to agree with their decision this time.
Free speech does not guarantee a platform for your speech, nor does it guarantee that you are able to say the things you want to. Even setting aside "private vs government", it doesn't even guarantee that the government won't censor you. It guarantees that you will not be arrested (by the government providing you with this right) for things that you do say. Even this has a few exceptions, e.g. incitements to violence…
My point was "free speech" is not synonymous with "The 1st Amendment". The former is a general concept and the latter is one way we protect it in the United States.