Immunity from what? COVID? Biden is president. He can pardon himself. No way he would roll the dice and risk his replacement losing. If he quits, he’s giving himself a full pardon beforehand.
If Biden resigns because of dementia a case could probably be made that he lacks the capacity to provide pardons. While he may do it they would likely want the new president to reapprove them so there is no question of their legality
They may be negotiating that the VP resigns as well opening up the entire ticket to a New Democrat team. That would make Mike Johnson President.
NOT SURE HE CAN PARDON HIMSELF