Chosen Solution
Touch ID sensor is reported as not supported upon reassembly of the iPhone 6S Plus with iFixit New replacement screen. I transferred the original home button onto the new screen. The home button itself registers pressing, but isn’t attempting to read fingerprints. Do I need to transfer the original camera/earpiece as well to have touch ID?
I’d try testing the home button back in the original display if you can. If it works then you know the new screen is defective, if not it’s likely the home button is damaged.
Make sure everything is connected properly. You shouldn’t need the original camera/earpiece. If it still doesn’t work it’s probably a bad home button extension cable on the display. I would RMA the display you got and try another one, could be just some defect. Alternatively, you may have damaged the chip on the home button, which would be irreparable. But a bad connector on the display seems more likely. Edit: I forgot, it could be the camera/earpiece in theory, but you still shouldn’t need the original, the new ones just might be bad. Either way, I’d get a warranty replacement.
As others have stated, if you are lucky, it’s just a bad home button extension cable. You have to be rally careful about where connectors are seated as even a little pressure in the wrong spot can cause Touch ID not to work but the button will still register a click. You could also try re-seating the home button cable on the connector. I ran into Touch ID not working but the button still registering a click on some phones when this happened. Try it with the old screen. You only need to have the home button connected to test the old screen.
