Driving (me spare) Focus redux

have a driving focus (previously ranted about on these pages). when connected to carplay, the dnd is automatically enabled. also have it configured to enable when connected to a car stereo by bluetooth. one of my vehicles has a bluetooth head unit. no dice. even told the phone it’s a car stereo. no matter, driving focus is not enabled.

i must be missing a trick – it can’t be an apple bug, can it?