The Face ID notch on the iPhone 13 series was reduced in size. Face ID is linked to the phone’s screen panel, so replacing the screen will disable the Face ID system. This was not made public, however.
Chips the size of Tic Tacs can be found embedded in the flexible cable that connects the screen to the motherboard. Previously, there was no such chip, so this was not a problem. If you go to an authorized Apple service center or shop, they have access to special tools that allow a new screen to be programmed into your device.
There is only one way for non-Apple repair shops to keep Face ID working – desolder the chip and resolder it onto a new screen. And this is where things get a little dicey. Above, you can see the chip next to a grain of rice in comparison to its size.
Finally, here’s a picture of the chip being taken out of the motherboard. When designing complex chips that require a lot of connections, a BGA is the best way to go. Given the size of the project, this is not a project that can be soldered by hand
It’s only a handful of repair shops that have developed tools and trained their technicians on how to do it, though. It’s still a time-consuming, finicky job compared to what it was before.
The possibility exists that this was a mistake and that Apple will release an iOS update to fix it. A similar thing happened last year when the iPhone 12 cameras were swapped out – they didn’t work at all at first, but an update was released months later that allowed them to be used again (though it showed a warning message).