Chosen Solution

Are the back glasses for the iPhone 8 and the SE compatible, and if not, how do you tell the difference

The main issue isn’t the compatibility. How these backs are built means you need to worry more about the camera cutout, as Apple welded the camera lens around the glass for a seamless look. That said, the iPhone 8 and SE 2 chassis are basically going to be nearly identical (the SE just uses the iP11 SoC, and a different board) but if you can get a piece of iPhone 8 glass with the proper cutout don’t chance SE 2 glass being incompatible. It’s basically built on old parts the R&D is paid for on, but you still want to check since Apple will change things like that and totally break parts compatibility for fractions of an inch.