According to the leaked press release, the feature is more about setting the initial focus point, but does not continue to follow your eye after the initial acquisition of focus. After the initial focus point is set, tracking works as well (or poorly) as it did before. At least that's what it sounds like:
"Featuring a new 5.76-million-dot and 120fps blackout-free1 Electronic Viewfinder, the EOS R3 camera will provide photographers with the ability to
select the initial area for AF tracking by simply looking directly at the viewfinder location where they want to begin AF. With Eye input AF2 and Servo AF activated, the camera will focus on and track moving subjects at that location in the frame. When Face Detect + Tracking is active, the camera will continue to follow moving subjects around the entire active AF area."
1 Blackout(s) may occur in some cases; such as when the built-in memory is full or when the flash battery is fully recharged after the battery ran out during continuous shooting.
2 Effectiveness varies depending on the subject. In some cases, dogs, cats or birds may not be detected, while some animals other than dogs, cats or birds may be detected.
A few ours to go but thanks to an anonymous tipster we have the Canon EOS R3 press release for the the one that's born to rule
www.canonwatch.com