I have started working out with a Tacx trainer (Flux 2) and overall am very happy with it. The integration that was added between the Tacx app (desktop, and mobile) is seamless and easily brings workouts over into Connect. It looks like a couple of years ago Garmin added partial support for the Physio TrueUp function, so the activity is sent to my watch (Forerunner 955) where partial performance metrics are computed (training effect, load).
Will Garmin be adding more complete metric computation at some point, particularly VO2Max? I have a a Garmin trainer, Garmin watch, and Garmin HRM Pro+, so I'd assume that all of the necessary raw data is present for this.
As of now if I want to get full metrics, I have to record the Tacx workout on my watch. The only downside there is that the speed and distance values are off (very low for a given cycling power versus real world and the Tacx app). It is not the end of the world, but I'd be even happier if the workout was able to be processed for full performance metrics!