Chosen Solution
So, I replaced my iPhone 6 cracked screen with a front panel assembly kit that includes the camera and earpiece. Everything works after the replacement fortunately, except for one: my screen brightness won’t auto adjust even if Auto Brightness is on. I have tested the front camera, ear pieces, and that the screen auto turns off if close to my ears while taking a call, and Touch ID also works fine. So I’m wondering what might be causing this, as from my understanding both the front camera and sensor use the same connection cable, but camera works fine while auto brightness doesn’t. Thank you for your responses :)
My advice is to take the front camera cable from the old screen and use it on the new one. Sounds like a bad front camera assembly that was preassembled with the front panel assembly kit. If you want you can contact iFixit for warranty issues like that for the screen.
