A very nice and comprehensive review overall but I'm a bit confused about their take on the EVF:
"Nikon Z9 Viewfinder Blackout
At fast burst rates like 20 FPS, a common concern with cameras today is the question of viewfinder blackout, where the EVF or LCD go black each time a picture is taken. A similar concern is when cameras only show a slideshow (usually delayed) of the high-FPS photos that you’ve just taken, rather than a truly live view of the action. Both of these issues can make it difficult to follow along with fast-moving subjects like birds in flight, leading to missed photos.
The good news is that the Nikon Z9 does not have either of these particular issues, as I noted in the prior section of this review regarding the camera’s EVF. However, it does skip some frames in the EVF/LCD when you shoot a continuous burst of photos, making it seem like the camera is lagging or showing you a slideshow, even though it’s not.
Ultimately, you can track motion with the Z9 quite well in high-FPS situations, because there’s no blackout or significant lag. But the viewfinder experience isn’t totally smooth when you shoot a burst of photos, so it may be slightly tougher than normal to follow along with fast action. (At 30 FPS JPEG bursts, the problem is at its most obvious.)"
https://photographylife.com/reviews/nikon-z9/4#:~:text=Nikon Z9 Viewfinder,of these particular
I have not had any problems with the EVF at all and after the 120 hz update, it feels even better...