I don't believe Bluetooth would have the bandwidth for screen mirroring, but wifi in such close proximity may.
USB-C is a fairly robust connector, in my experience. If that's actually a hurdle, a cable that utilized a magnetically connected adapter on the phone end could be used. Plug the adapter into the phone once, and use the breakaway mag connection; the remote display could have a native mag connector. That's
already available.
I haven't utilized AndroidAuto in many vehicles. Like I said, I've had no problems using a Pixel 6 phone over a USB-C connection with an OEM Honda (made by Pioneer, I believe) head unit. From what you and
Ridefreak have said, I can certainly see automakers mucking things up in an effort to protect their profitable in-house solutions. If an industry leader like Apple, Google, or Microsoft pushed past those problems with their own solutions, maybe automakers would be pushed away from their proprietary protectionism.
From what you said about Waze, that's a Waze problem.
If you haven't tried Google Maps lately, you may be surprised by the progress made in the last few years. I still have a Garmin dash GPS because I like the way it handles lane designations in high traffic areas. At the time I purchased that Garmin, Google Maps lacked that feature, and the general interface didn't work as well as the Garmin unit, as you said. Today, Google is simply better, with more up-to-date maps, POI searches, and lane designations. My Garmin offers voice command as does my phone, but the phone based search capability far outclasses the relatively meager library stored in the Garmin.
The main advantage of a dedicated Garmin unit over a phone is in areas that lack mobile network coverage over wide areas when you didn't download maps for offline use, and those areas are becoming ever more rare in the continental U.S. Outside that area, I'd probably want my navigation device to use stored maps, and there are several ways to make that happen with a phone, too.
