I have little sympathy of Musk's way to dealing with his latest purchase. But regardless, saying that "freedom of speech means that government cannot tell people what they can and cannot say" is a misdirection. The principle was conceived in the times when nobody except government could enforce censorship. This principle works when the venue for the public discourse is a town square, funded by local taxes.
In this day and age though, when we collectively handed the "venue for the public discourse" to businesses, that are financed by advertises, it means that advertisers decide what can and what cannot be publicly said. Yes, it's not a limitation of the freedom of speech in the narrow legal sense: it's not the government that does the limiting. But the result is still the same: there is somebody who decides what it "OK" to say in public, and what is "not OK".
As long as the "venue for the public discourse" is a business, there cannot be true freedom of speech on that platform. (Even if it is funded by member subscription, it will be prone to the "dictatorship of the majority".)
(For the record, I've never had a twitter, or facebook, for that matter, account.)