Bluetooth Calling Problem

[acronymy]

Conversations does not play well with Bluetooth calling.
I have tested Conversations and Cheogram in two different brand vehicles, problem is identical.
If I am playing regular radio in vehicle and make a Bluetooth call, sound comes through vehicle speakers correctly as expected.
If I am streaming media from phone and make a call, the vehicle screen does show call in progress but call sound comes through on handset only. (same behaviour for incoming calls)
Switching source back radio in vehicle is not a solution, as once problem has occurred once when streaming media then same problem now exists when switching source back to radio.
Road trips listening to podcasts or audiobooks and Bluetooth calling with Conversations is a bad user experience.
Please note:
Signal messenger Bluetooth calling always functions correctly and perfectly in any and all situations with same phone and vehicles.
What did Signal get right that Conversations did not?
Pixel 8
Latest GrapheneOS

[licaon-kter]

/close this, we'll continue on Codeberg