I found a solution guys!!
For me when fiddling with the magnifying, once I can get it to 0.5x the back camera turns on. (Tap the magnifying number while on the back camera) Is a bit fiddly but it works. I’d guess apple thru software shuts off the back camera if it detects some hardware issue. (My phone is a bit beaten so I wouldn’t be surprised but curious if you guys have good condition phone that have this issue or are like me and have potentially water or fall damage like me) it’s more of an work around to apples software than a solution but it somehow bypasses whatever the iPhone is trying to do. Maybe a camera expert knows about if changing magnifying changes some detectors because that would probably be the issue. (I have ios15.6.1) Anyways God bless, have faith in whatever god has for your path and I hope it work