Every 6 months or so I go looking for a solution to this problem and still haven’t found one.
When my phone (Pixel 7) is connected to my car by bluetooth, the phone itself will not make any notification sounds. It is attempting to send all notification sounds to the car. The problem is, if I am currently not listening to any media and the head unit is off, I will not hear anything at all. The only possible way to hear it, is to have the head unit on and set to bluetooth input whether or not I’m listening to anything. This was not always the case. I think it changed after Android 13 was released but I’m not 100% sure.
In my state it is against the law to hold your phone while you’re driving so I keep it connected by bluetooth for calls. It’s not a problem when I’m listening to music or podcasts which I frequently do. It’s only an issue when I’m not listening to anything. I’ve looked into updating the car’s software but it’s already on the most current version.