I don't entirely agree. Obviously on a legal level sure, Trump has no right to use Twitter.
But I do think its fair to be concerned with the amount of power and influence that big tech companies like Twitter and Facebook and Google have on the public discourse. My problem here is that on the right it seems that some are simply mad that the unrestrained corporate power that their political establishment helped unleash is now hurting them but instead of questioning that approach generally they merely want to narrowly regulate big tech so it can't screw them specifically in this very particular way.
To be fair there are right wing populists who have a generalized anti-corporates messaging but even there often the corporations they name and target are those that are perceived as left wing(traditional media corporations, big tech etc.).
My solution off the top of my head would be for the government to just buy a controlling share of these corporations so they can set the corporates policy for them specifically instead of passing laws that would affect all social media and forums on the internet. But I can imagine there are potential problems there,. For instance, is being banned or otherwise moderated by a corporation that is majority owned by the government a 1st amendment issue? So idk, could be more trouble than its worth.