@Amber, that’s not how Android Auto works. The head unit in the car is basically just an additional touch screen which some apps (which have to be certified by Google) can use. But everything runs on the phone. The head unit can’t do anything without the phone.
@Benoist_Hitier, unfortunately, Android Auto is a proprietary Google product and not part of the Open Source Android code. If you want to use it, you’ll have to go with Google.
There are third-party apps which can mirror the phone’s screen to an Android Auto head unit. These might work without Google services. You won’t have the Android Auto experience, but you can use the (larger) screen in the car to operate the phone. This is more like a hack, so you would have to do some research into the status quo.