Tacx Neo Smart Bike Fan Control

I’ve got a Tacx Neo Smart Bike, which I connect to my iPhone or iPad.

I set the fans to Fixed Speed in the Tacx app, and they fire up.

Then in Zwift, if I free ride, the fans continue.

But if I do a workout, Zwift seems to take the fans over, and controls them via Power Output.

Am I doing something wrong? I can’t find settings in Zwift to sort it?