rear camera not working, even after replacing with another

Hi there, I bought an iPhone 11 pro max from a local gentleman knowing that the rear camera was not working. Figured for the price, was worth a shot and it still most definitely wasn't a bad deal. It's the camera app stays black issue, which doing a search, isn't too rare. Even after replacing with another rear camera, same thing persists. 3uTools says that the camera isn't working and might be damaged , however, the phones in pristine condition and I'm sure I'm the first person to open it up. I've searched the web before posting here and got the same troubleshooting from ever site and tried them all a few times. Reset all settings, reset entire phone, recovery, updated to latest iOS, force closing camera app then reopening, swap from from facing camera (which does work) then back to rear. And now the last thing I've tried was relacing entire camera with another oem and same thing. I'm at a loss for a solution now and assume it's sone sort of motherboard Issue?

P.s. I managed to get it for a split second to work with the switch to front, wait a second, then back to rear technique, but only for a second .

Any help is appreciated, thanks I'm advance.