Is the front facing camera working? Or is it just indicating Face ID disabled? Face ID does require the front facing camera to work in order to work.
I would try powering up without the rear camera connected and see if you can at least get Face ID that way. A faulty rear camera can cause all kinds of issues.
No flash is normal for a non functional rear camera since the flash enable signal comes from the camera.
If no camera even then, I would start to question if it's possible that there is a board level issues.