I noticed the same behavior in my Vision Pro the other day. The conclusion I came to was actually that I was not seeing the boundaries of foveated rendering, bu

I noticed the same behavior in my Vision Pro the other day. The conclusion I came to was actually that I was not seeing the boundaries of foveated rendering, but a UI element. When staring at touch targets, it projects an overlay over the target with a slightly bright large circle around your eyes, fading further away from your eyes. As you move your eyes around, the circle follows them. This is particularly noticeable where a very large touch target (like a large text box) is present, you can easily see the entirety of the circle overlay, whereas with smaller targets it’s cut off on the edges of the target. It also happens to align with the foveated rendering downsampling circle because of course they both follow your eyes. I’m guessing this is what is happening here. To test this myself, I looked around on a large, lighter colored page in safari with no large touch targets, and could not see the same circular glow.