@Flynn_Goodger, yes using the ‘virtual run’ activity will allow Zwift to pickup heart rate, as I can only suspect that the ‘virtual run’ activity allows the OHR to be broadcast via BTooth. Again, I am currently using the ‘virtual run’ activity when i ride on my indoor trainer.
Furthermore, please put comments and feedback on Garmin Forums to help promote these changes to be made sooner than later. Here is a link to a suggestion i’ve made on Garmin’s forums. Where is the Virtual Cycle or Virtual Ride for Zwift Users? - Accessories & Sensors - Cycling - Garmin Forums