The private property rights that give private companies the ability to censor your speech are created and inforced by the government in the first place, so functionally it's not different. A handful of massive companies who functionally own the government getting to police what is acceptable speech is not functionally different from the government doing it directly.

I really can't fathom why people cry about "freedom of speech" when something privately owned decides not to include what they consider fucking shit. Freedom of speech is the fact the government cannot stop you from saying what you want. NOTHING ELSE. People paying to run their own instances do not owe you anything

All rights are only between an individual and their government

Different rights have different scopes. Some rights, like the right to live, are between everyone. Some others, like the right to receive a purchased product, are only between buyer and seller. Freedom of speech "just happens" to be between individual and government, in countries where it's even a right.