@ged_hickman1 - after some more tinkering, I got it to work!
The combination that did the trick was:
- Mac OS Prefs - make sure to select the Bluetooth output device
- Roon Zones - make sure to select the System Output zone
What I can’t recall is which of the System Output settings at first caused the issue, or whether there was user error of sorts involved. Either way, I got what I needed.