Turn on the iPhone flashlight, it's working, so it's not the problem of the iPhone flashlight.
Turn on the iPhone front camera; the iPhone front camera is working properly, so it's not the problem of the iPhone front camera.
Seems the iPhone back camera problem wasn't caused by external accessories, therefore, we need to check iPhone motherboard.
Use UT139C Digital Multimeter to measure the iPhone rear camera connector, a circuit signal measured is 0L, which is abnormal, it's disconnected.
Assemble the iPhone 8, turn on the iPhone, and then test the iPhone rear camera, the iPhone 8 rear camera can be turned on smoothly, the camera function is working perfectly.
In this way, the rear camera of the iPhone 8 is repaired. If you can't fix it by yourself, you'd better go to the nearby Apple after-sales shop for repairs. There are other iPhone issues, please leave a comment in the comments.