Screen turned black but device works (including touch screen)

I've had this problem for a couple months now. Basically the screen turned black but the entire phone including the touch screen keeps working.

Usually it just needed some squeezing, light hitting it with my hand or forced reboot to return working, but I have not had any luck this time.

I have swapped the original screen with a new one, but it didn't solve the problem. When I opened the back cover, some screws fell out and the others were quite a bit looser.

I can currently access the phone via usb debugging (mirroring the screen) using a script called scrcpy.

I have tried anything I could (cleaning the LCD pads, swapping back and forth the original one, disconnecting the battery, etc.).

What could possibly be the cause?

Just in case I have the USB daughter board on order to hopefully solve some other problems (phone disconnecting from windows when accessing big files, android auto not working).