IPhone does not connect phone calls to bluetooth while playing music on it.

I'm in my car, playing Spotify over the, bluetooth handsfree equipped, radio from my iPhone 12 pro, getting directions from Waze in between. I get an incoming telephone call, this call is then transfered to the iPhone internal speakers and not the radio handsfree set.

This means I have to take my eyes off the road and switch the call to bluetooth to take the call or let it go.

This is relatively new behaviour, the phone used to just put calls straight through to bluetooth. I don't know when this started, could be a year or so because I forget to search once I get home and I don't get many calls anyway, but when I do I would like to have them on handsfree and not have to fiddle with it.

Is there a setting somewhere? I couldn't find it.