Trump can pardon himself all day long but are there not other serious items at large from before he entered the White House?
There probably are, maybe even more than arose during his term. But I think he can pardon himself for any federal crime up committed up to the date of the pardon. As pointed out, it doesn't help him if a state goes after him, and doesn't prevent civil cases like the defamation case that he's been sued over.
Also, all of this assumes that he can actually pardon himself, which I'm not sure has ever been tested.