DIAGNOSIS It's not broken. The '1ms MPRT' setting is a backlight strobing feature (often called 'VRB' or 'Motion Blur Reduction'). It pulses the backlight to reduce motion blur, which causes visible flicker and reduces brightness significantly. This is normal operation.
FIX Simply turn it off. Press the menu button, navigate to the 'Game' or 'Picture' settings in the OSD, find the option labeled 'MPRT', 'VRB', or 'Response Time'. Set it to 'Off' or 'Normal'. Your screen brightness and flicker will immediately return to normal. For most users, the 'Fast' or 'Faster' response time overdrive setting is a better balance of reduced ghosting without the severe side effects.
IF THAT DIDN'T WORK If the extreme darkness and flicker persist even after turning the MPRT setting off, perform a factory reset on the monitor. In the OSD menu, find the 'Others' or 'System' section and select 'Reset All'. This will clear any conflicting settings.
HEADS UP Backlight strobing (MPRT) is known to cause eye strain and headaches during prolonged use. It's a trade-off feature for competitive esports, not for general gaming or desktop use. Also, it often disables adaptive sync (FreeSync) and brightness controls while active.