I think you are correct that it’s the car’s fault. I have an MPOW brand Bluetooth adapter that almost always works properly with my phone. I use it in my Mazda 3 that doesn’t have Bluetooth built in. My 2017 VW Golf (one year older than the MPOW adapter) does have Bluetooth and it frequently gives me trouble. However, I’m typically able to get the connection to work by disabling then reenabling Bluetooth on my smartphone. Resetting the VW head unit typically doesn’t help, which is the opposite of what I’d expect if the problem was with the car. The VW has Android Auto over USB, which I thought would be the end of my Bluetooth woes, but that has enough of its own problems that I just keep putting up with the Bluetooth.