Locked iPhone- no way of recovering

Hi- we allowed our son to set up his own iPhone about 3 years ago for an iPhone 8. He has forgotten his Apple ID and has no way of resetting this as he is also locked out of his email with yahoo which was the recovery account and all connected phone numbers to both email and Apple account. Basically, we have set him up a new phone and had to accept his old phone is useless as he can’t prove his identity… his old one is worth money but we can’t unlock it to sell it on. Is there any way of requesting a phone unlock?