The nomination is obviously his if he wants it, and there's no reason he won't run. He'll just spend the next four years criticizing every move of Biden, and run by claiming Biden was a disaster.
Hating the presidency, for one thing. Being entangled in literally all of the legal disputes, for another.
Seriously, I see no reason why this guy - who never wanted to be President in the 1st place, then hated being President each & every single day of his term but only stuck around because being an incumbent offered him temporary immunity (through certain statutes of limitations, too) & because he views being a quitter as an even weaker attribute than being a loser - is gonna voluntarily try & go for it again when he can just as easily grift off his teasing of the deplorables about how he might run (when, for the aforementioned reasons, it feels obvious that he actually won't).