Pixel tablet is an interesting option to consider. There are also head units available which run (non-Android) Linux (and support android Auto / Apple Carplay) which could be options depending on OP’s needs. Either of these options might satisfy the “tainment” half of “infotainment” but I’m not sure how well they would accomplish the “info” half of the equation.
I have only basic knowledge of MicroG, but isn’t it only necessary (on a phone or tablet) if you want/need functionality that comes from prorietary Google apps (e.g. Google Play Services) As far back as I can remember LineageOS/Cyanogenmod and other early alternative versions of Android were usable without MicroG and without GAPPs provided that you are satisfied with the functionality provided by AOSP alone.
I’m not quite grasping the relevance of MicroG in this context but it’s probably been at least 5 years since I last read up on MicroG, so its likely i’m misunderstanding or forgetting something.
I’m not sure how relevant this is but the Wiki article for Android Automotive does state that:
Android Automotive is an open source operating system and, as such, a car manufacturer can use it without the proprietary Google Automotive Services (GAS)—which is a car equivalent to the Google Mobile Services (GMS)