Chosen Solution
I repaired an iPhone 11 it was a screen replacement and back glass replacement with the forward laser machine everything seemed to work fine but when the phone is on for a couple minutes the phone turns off and back on. After it randomly restarts it acts like normal until a couple minutes have passed it does it again. I’ve tried a different battery and even the original screen but it still does this. I’ve also disconnected the front speaker flex in case it was causing problems but it still does it. I put it into dfu mode and updated it successfully now its on a white screen that says attempting data recovery but it keeps turning off before it finishes any ideas on how to fix this power off problem.
In this case, the charging flex or the microphone/flashlight flex next to the camera might be damaged. These contain sensors (prs0 and mic2) that cause the phone to restart after some time if no valid signal is received.
I had the same problem with a iPhone 11 tried everything last resort is changing out the battery
