I'm afraid Google disagrees with you:
Plugging in is great for road trips, but for shorter drives, wireless is the way to go
www.androidpolice.com
Android Auto brings apps to your car display so you can focus while you drive. You can control features like navigation, maps, calls, text messages, and music. To get more information about your
support.google.com
Yes, you can plug in a USB cable, but if you are using wireless AA, then in addition to the standard Bluetooth connection, the phone also connects to the head unit via Wi-Fi automatically (negotiated via the Bluetooth connection) in order to have enough bandwidth to handle drawing the display on the head unit's screen.
"5G" and "5GHz" aren't the same thing. "5G" means "fifth generation" and has nothing to do with a frequency/wavelength. A 5G signal can use lots of different frequencies depending on the cell company (Verizon vs. AT&T, etc.) or country. See
https://en.wikipedia.org/wiki/5G_NR_frequency_bands for a list of all of them. You are correct that there are differences in the signal properties based on the frequency (range, building penetration, etc.) but you can be connected to 5G using a very high frequency connection, or a low/midrange frequency, and potentially both at the same time (
https://www.nokia.com/about-us/newsroom/articles/5g-carrier-aggregation-explained/).