FWIW the last Garmin “VO2max” session was a workout a few weeks ago. That workout had 24 minutes of threshold, performed outside, so vaguely looks like unstructured over/unders. And WKO estimated I spent 21 minutes above 90% VO2max and 90 seconds above 95% VO2max. And my post-workout notes state I was doing a lot of “huffing and puffing.” Given the WKO analysis and my notes, I agree with Garmin’s classification as VO2max.
In other words, VO2max is not a power or heart rate zone. And without wearing a portable mask to measure oxygen consumption, you need more sophisticated analysis tools to determine if it was a VO2max effort. And a couple weeks ago those tools agreed with my own self-analysis of breathing associated with being in a state of near maximal oxygen consumption.