Someone else filed the application for him, and that application includes a fresh email address for this purpose. There is no reason to deduce from this that Musk had anything to do with choosing Protonmail, that he intends to read the mail directed there, that he is otherwise a Protonmail user, etc., etc.
Judging by the @america feed on twitter it will be all of the fascism with none of the fake MAGA populism. Good luck finding a constituency for that outside of a handful of billionaires and their groupies.