For indoor rides, you only option is Zwift → Strava → Intervals.
Garmin wont sent Zwift rides anywhere.
if you dual record, then you will get Garmin → Intervals but it will not have distance / Speed and all the other stuffs from Zwift. It’s 2 separate things. AFAIK, no way to consolidate the 2 of them unless you do it manually via some apps to merge the fit files.
If you’re on iOS, I have a feature coming up soon.