Not fully open source,
but less proprietary crap.

AA4MG (Android Auto 4 MicroG)

It allows to run Android Auto with:

• MicroG, open source alternative to Google Play Services)
• Empty stub APKs, for the other Google Android Auto dependencies (e.g. Google Maps, TTS Text To Speech, ...)

That way the only proprietary thing you need,
is the actual Android Auto app,
not it's hand full of sketchy propriety dependencies.

Full disclosure: I helped develop AA4MG + AAXLU :)

Bluetooth audio device to aux in on my car with phone mounted on the dash is my privacy respecting solution. Work great for all my needs. And yes, as far as I know Android auto is indeed a privacy nightmare. It allows lots of access to your phone and use of your phones internet.

I don't really believe so. Auto manufacturers have to specifically put Android Auto (and apple CarPlay) onto the firmware that lives on your cars system. Finding something that interacts with one of them without actually using that software seems extremely difficult or even impossible.

It may be done, possibly, but I imagine it would be extremely limited.

Well... about 20 years ago it was not THAT uncommon for nerdy / techy people to put a small Linux powered PC into their car for all sort of things. I personally had a system build around a passive cooled Transmeta Crusoe based board running on some Suse Linux sitting under the passenger seat of my Escort Mk 4 back then...

I think with a Raspberry Pi or similar system you could build something very interesting today with a much better user experience

• Buy a phone that can do display alt mode over USB.

• Buy a usb C display.

• Mount the display in the car.

• Connect to your cars bluetooth audio.

Viola!