Bluetooth is needed for the phone and texting (SMS). Pairing was never an issue.
The USB cable OR WiFi is necessary for the apps because Bluetooth doesn't have the bandwidth.
Sitting in the Trax, the fact there is no WiFi signal present (I have monitoring/scanning software on my Android tablet) is at the root of this situation.
In that I recall there was Wireless AndroidAuto in my Trax until the 30-day OnStar HotSpot trial expired is an enigma. That HotSpot uses AT&T, I think, and costs $50/mo. Yup, there's a SIMM in the Trax.
So, I believe when OnStar disabled it's HotSpot app, it turned off the WiFi radio. Which makes me wonder how many people reporting it worked OK were still on that trial (and never reported it breaking later in the same thread, if at all) or sunscribed to the HotSpot?
The wireless AndroidAuto and CarPlay lets your "phone" WiFi connect to your Trax. As this aspect of Car Tech is new to me, I am at a loss as to how this is enabled.
To connect your "phone" to any WiFi access device, you need to find that WiFi in settings (SSID name), select it and plug in a password (these days, no-password public access is practically non-existent).
I have a dash cam (Rove R2-4K Pro) that connects to my "phone" via WiFi to manage settings and view/download the videos. I have to find it in my "phone" settings (SSID is the cam's serial #) and enter the default password. This disconnects me from my home WiFi, of course, and Android informs "no internet available." Because the cam isn't the internet. When I'm done, I disconnect, find my router and reconnect.