Apple has updated the product comparison pages of the iPhones 8, X, XR, XS, se, and 11. They now support FaceTime at 1080p over Wi-Fi, as opposed to before when they only supported 720p.
Calls made over cellular will still be at the lower resolution. But if you’re FaceTiming over Wi-Fi you may notice increased clarity.
My sister has an iPhone 8 with the update, so I called her up on FaceTime. I also took screenshots on my iPhone 12 mini to compare what it looked like on my end.
The iPhone 8 still has the 7MP FaceTime camera, as opposed to the 12MP camera found on the iPhone 11 and later. Whether you see a difference depends on how sensitive you are to changes in video quality, or how good your eyesight is.