Nearly two years after my last attempt to get Android Auto working with a rental car on holiday, the same phone and one of the same cables Just Worked with a different car:

Android Auto on a car display

All you do is plug in a USB (C to C) cable; you have to click through a small disclaimer about how it’s not their fault if you crash, once, the first time any given phone is paired.

I’m very late to the party on this but it does exactly what you’d expect, with the car acting as a thin client for the phone and various apps using the extra capabilities provided to integrate nicely with the car display, buttons on the steering wheel, etc.

Realistically, car manufacturers need to can their own efforts to make sat nav software and suchlike things and leave it to the experts. Just support this (and the Apple equivalent).

This particular rental car had a completely digital dashboard too, but they obviously hadn’t implemented the APIs for Android Auto to use that too - the only slight downside as I personally prefer not to have to move my head to see the nav map.