Exactly, “on his own accord,” you are 100% correct, if Trump decides he ain’t leaving, he ain’t leaving, regardless of the Constitution or any other applicable entityTrump will, on his own accord. He's not interested in running again.
Plus, the 22nd Amendment doesn't allow Trump to serve a third term.
Who is going to stop him? Not the GOP, not the SCOTUS, not the right wing media, not social media, not the Red Hat Club, in fact, all of those will actively support his decision. His only hurdle would be the media, and as we have seen, he is working now to limit and curtail that media