Would he really give up the governorship to become Attorney General? I don't really have a grasp on what Cuomo's ultimate ambitions truly are, but it somehow seems like an odd career move given how difficult the task of the next AG is going to be (particularly because he/she is going to inevitable earn some really intense vitriol once steps are taken to repair some of the damage caused by Barr).
If Democrats get supermajorities in the state legislature this year, his power is much diminished. That would be a strong incentive.