Even as a well trained software engineer who works on transportation software including ECUs (heavy equipment not cars), I'm not sure there is much I could do with root. IF I had full source code to my car's radio I might try to add android-auto back in (it has android-automotive so I know it can do it), but if that isn't easy I'd probably give up. Without source code and a lot of time doing anything is impossible - as anyone else who works on complex software knows.