It is common that the screen goes blank after customers fix Z Flip 5 inner screens. The Z Flip series uses a magnet in the hinge to detect when the phone is opened or closed, which in turn activates the corresponding screen. If the magnet from the original screen wasn't transferred or properly installed in the new screen, it can cause the front display to remain black.

Unfortunately, the magnet is just right under the frame, so it makes customers very difficult to remove it from new screens, as it could damage the display. As per the photo below.

The best solution is to remove the magnet from customers' broken screens and cut it into a thin and flat magnet, then put it under the motherboard. As per the photo below.