A private company regulating the private speech on its privately owned social network is not a First Amendment issue. In fact it is precisely the sort of thing

A private company regulating the private speech on its privately owned social network is not a First Amendment issue. In fact it is precisely the sort of thing that the First Amendment exists to protect. Facebook and Twitter are not constrained by the First Amendment. The First Amendment exists as an umbrella under which they can do whatever they want. In this case the federal government (which is constrained by the First Amendment) is the one proposing to ban an app—entirely. That is most definitely a First Amendment issue.