You can't cut Carr next year, so who can fix him?

I don't think he can be fixed. The best course of action is to the best rookie QB you can get and you go into camp with Carr as your starter. You might get Carr for another year but the transition will already be underway. Or if the rookie is ready, you only have Carr around for that one season.
I tend to agree. The Carr and Wilson situations get compared, but I don’t think it is the same. I posted this elsewhere when someone said Carr can be brought back to life like Wilson:
Wilson has a better track record than Carr, even if he isn’t who he used to be. How many seasons did each QB have at least 30 passing TD’s?

Carr 1 (back in 2015)
Wilson 5

How many seasons has each QB had a TD % above 6%?

Carr 0
Wilson 9

A QB rating over 100?

Carr 2
Wilson 8

Hackett couldn’t get the best from Wilson, but it’s harder to say that we aren’t getting close to the best of Carr. He has always been a coach away from greatness his entire career, and now we’re the team trapped in that cycle.