I did a VO2max workout in Zwift this morning and got 0 intensity minutes in GC.
Looking back though my GC calendar, I have not been getting any intensity minute credit during indoor (Zwift) rides in the past month. October 30th was the last indoor ride that I received intensity minutes from. I have had multiple outdoor activities since then with intensity minutes, but none of the indoor rides have. Zwift is synced directly to GC.
I don't necessarily track intensity minutes, but I don't know if they are used in other behind the scenes calculations so just throwing this out there...