Well, maybe. MNN is a public access TV channel with an exclusive franchise agreement with the New York City government, yet the SCOTUS recently declared it wasn

Well, maybe. MNN is a public access TV channel with an exclusive franchise agreement with the New York City government, yet the SCOTUS recently declared it wasn't a state actor for purposes of the First Amendment. As the court wrote, "the City’s designation is analogous to a government license, a government contract, or a government-granted monopoly, none of which converts a private entity into a state actor — unless the private entity is performing a traditional, exclusive public function." Since it's unlike that Twitter can be considered to be performing "a traditional, exclusive public function", it's unlikely they'll fall under that provision.