It sounds like there is an issue with the display you installed. Are you sure you installed the correct display? If an incorrect model display was installed, it may appear to be functional but will have issues with component functionality such as the camera, backlight, or TrueTone. I've accidentally installed the wrong model display before and everything was functional except for the camera. Alternatively, it's possible the display was damaged during installation. Was the battery fully disconnected when you installed the part? Did you have any difficulty during the installation? Do you have another working screen you can test with? Good luck!