On Friday, January 8, 2021, Twitter banned Donald Trump from its platform.
"After close review of recent Tweets from the @realDonaldTrump account and the context around them we have permanently suspended the account due to the risk of further incitement of violence. In the context of horrific events this week, we made it clear on Wednesday that additional violations of the Twitter Rules would potentially result in this very course of action."
Because social media companies are private entities, they can decide what they want to publish and not publish. A person cannot force social media companies to publish their content under the First Amendment.