I think he will be a 49er next year, if they had a QB, they'd be a dominant team. Jimmy G is a very good, albeit often injured game manager.
Mayfield needs to spend a year as a backup to a solid QB coach. The Rams, Raiders, and Jags come to mind beside the 49ers. Bengal and Chiefs too.
What he did in Cleveland early showed her has the skills, but he's not in the head space to play now