In First Amendment jurisprudence, there is a very specific bar as to when government involvement becomes unconstitutional coercive state action. That bar requires direction from the government and a (potentially implicit) threat of government action or retaliation if compliance is not met. Bellyaching about what a company or individual doing doesn't meet that bar, otherwise pretty much every single congressional hearing would be illegal.
As far as I'm aware, no one has yet produced any evidence that the US government reached that bar with respect to Twitter. There's definitely been several lawsuits that have attempted to allege this--and some where the judges tried to push the plaintiffs to actually properly allege this--but nothing has ever stuck, primarily because everyone filing these suits seem to think that the government looking in a social media company's direction somehow makes it automatically a First Amendment violation.