Trump cannot claim that his personal twitter account is solely his personal opinions and thus can do whatever he wants with it, whilst at the same time using it

Trump cannot claim that his personal twitter account is solely his personal opinions and thus can do whatever he wants with it, whilst at the same time using it as a platform for public policy announcements and political speech. If instead he had two accounts, one in the capacity of the POTUS and another as his own, then you may have a point. But that isn't the case.