I can't directly answer the question. However, I think what complicates this issue is the political actors involved. Twitter may be a private platform, but when the President posts a Tweet, that is very much a public, political, government message.
For example, a federal judge barred Trump from blocking followers, despite Twitter being a private platform.
https://www.cnbc.com/2018/05/23/trump-cant-block-twitter-fol...