I can't say I really know.
Since I posted this I've managed to get it working in a Fusion VM test install on my M2 MacBook, but I'm not entirely sure how. I posted this having failed to get it to work on my MacBook, but then it started working. So I've remoted into the mini at home, installed Fusion and HA, and am in the process of restoring the HA backup from last night, so when I get home I should be able to plug the Conbee in and it will (might) work.