The Canon EOS R3 will come with eye-controlled autofocus, made most famous by the film camera, the EOS 3. There have likely been a few advancements in technology over the last few decades, but there are some similarities in how the system will be calibrated.
The USPTO patent US 2021/0124239
The first patent shows the menu system that will likely be similar to what we see in the Canon EOS R3. It looks like there will be a lot of customization options to improve the experience.
The USPTO patent US 2021/0125375
The second patent shows off how Canon plans to set up calibration for eye-AF on the Canon EOS R3. This calibration is similar to the way the Canon EOS-3 worked, you will follow a moving target around the viewfinder. Canon has likely worked out a lot of the issues with the first implementation of this technology. Most notably the struggles people with glasses had from time to time, as well as issues that weren't easy to explain.
There will likely be a lot more patents over the next couple of months that will better explain how the Eye-AF will be implemented in the Canon EOS R3.