First off I have never been able to wear my Garmin watches when using Zwift. I have found that the bluetooth signal from the watch can interfere with the signals from my trainer and HR monitor, causing intermittent drop outs and interference. That has been the case with both my old Forerunner 45 and my newer Forerunner 55. I have also tried recording an indoor bike ride on my watch while riding Zwift, but then the Zwift ride does not show up on Garmin Connect. I've learned to deal with that problem by plugging in my watch to charge, on the opposite side of the house, while I do a Zwift ride. Then the Zwift ride and all of its data gets loaded into Garmin Connect and there is no problem with signal interference. I don't need my watch when I have a computer screen feeding me constant performance data anyway, so it's really not a problem.
The one nuisance factor about this is that the effort does not get counted in my Intensity Minutes. I guess only workouts recorded by the watch count towards IMs? Is there any way to include my significant (at this time of year) indoor cycling efforts in my overall intensity minutes total for the week?