This is one of the main reason for me to not install alternatives to android. I bought my car specifically with android auto because car integrated navigation usually suck, while Google maps works really well.
I think that android auto app is far from sufficient because ri connect to the auto heavily relies on Google services which have access to low level system.
Theere is an open source reimplementation of Google services (which is also privacy friendly) called microG, but I don't know if it plays well with way droid and/orandroid auto, but try to check it out. I'm sure you are not the only one trying something like that
there's a magisk module for microG Androids (https://github.com/sn-00-x/aa4mg) that brings in some proprietary AA stubs that work in that environment. It pulls in the necessary gplay dependencies (assistant aka velvet, tts engine(?) and Maps). You could use https://github.com/casualsnek/waydroid_script and load this module in magisk.
Then there's a thread where users assemble a patchset for ROM / Android GSI builders to use AA as a user app, making it more accessible than it being a priv-app - https://github.com/microg/GmsCore/issues/897
The waydroid gapps image comes with Google services. I'm trying to install from Google play, but it says my device isn't compatible. I've read that I have to self certify it in order to get Google play protect certification working. Maybe that's the problem. I'll try and see what happens.