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.
I use android auto and this has been killing me forever… Until about 6 months ago. I found this app on FDroid. AutoNotify. I was never able to get Signal notifications on the speakers when connected to Android Auto. This fixed that. Check it out. It works.
https://github.com/zehuanli/AutoNotify
Unfortunately I don’t have Android Auto capability in my car but thanks for the reply. Maybe this will help someone with a similar problem.