I'd think the use of an auto pen would be fine if controlled by the signer, but if otherwise, I'd think that is no bueno.
My profession is in/around Government contracting and anyone who signs documents has to have a delegation of authority letter which authorizes them to sign and legally bind the entity they are signing on behalf of. You can have multiple levels of delegation but I can't imagine the POTUS can delegate his authority legally if what is being signed has to be signed by the POTUS. For example, ITAR documents have to be signed by my company's Empowered Official, of which there is only one for us and it's not me, so I can't sign those documents even though I have authority to commit/bind the company legally. Only the owner of our company can sign those docs with the Dept of State/DDTC. There has to be a law that says ONLY the President can sign x, y, or z. Anything signed by someone else in those cases should be thrown out, but I'd be willing to bet the courts would try to claim intent and Biden was not opposed to what his name was signed to so it's all good.
Those are my thoughts. I'm not a lawyer nor did I stay at a Holiday Inn Express last night, so do with that info what you will.