- Edited
it is preinstalled on GrapheneOS
I checked its called App Store. Here a screenshot of the icon: https://imgur.com/0zsJNrA
you also install Google Play and Play services with that App.
make sure to uninstall the Android Auto installed with Aurora before installing it with the App Store app :-)
I am not sure but I believe some apps need to be installed with the Google Play store and not Aurora to work with Android Auto. I dont have any first hand Android Auto experience yet as my current car is too old to have any kind of Android Auto device installed.