The webinar I am referring to was a through Nikonians for members only. She was part of the initial launch, but for this program she had time to use her Z6ii. The program included tracked subjects in flight as well as subjects that were easy to follow or not flying. Michelle is a wildlife photographer but not just a bird photographer. She's photographing loons, geese, moose, small mammals, and similar subjects - as well as small birds.
The thing about blackout or lag is that it does not apply to all situations. There are plenty of situations where frame rate is very important. It is possible to follow a subject in flight using High Extended - it's just a different technique. We also need to consider that mechanical shutter is no longer silent - and that can be problematic.
I tend to take the view that for wildlife, Silent Shutter with High Extended is my mode of choice, and if there is a problem with a specific subject, I would consider dropping back to Mechanical Shutter and a slower frame rate. Some subjects are tolerant of the sound of the shutter, but many more are spooked by it. I'll stick with the fast frame rate provided by silent shutter for wading birds, shorebirds, and similar subjects that I can follow and track.