if you just want audio & your car doesnt support Bluetooth you could use an adapter to take it from Bluetooth to 3.5 aux. if your car is so fancy it doesn't have aux input you can get a Bluetooth to FM radio adapter that will take over one the channels in your car as well.
I actually don't know if newer cars can just use Bluetooth without an app. I've been thinking of replacing my car with something more practical which is why I posted this. I don't know how much privacy newer cars have left.
Unless it's changed in newer car models, Android auto only connects when you physically plug it into one of the provided USB ports in the center console/glove compartment. The BT connection only allows media and phone usage (audio and SMS). You won't get maps or other apps to appear on the in vehicle display, though.