Open the menu with the "OSD" button on the side of the monitor, and then find the "BRIGHTNESS" in "BRIGHTNESS" menu. Please note that after setting the brightness, you need to press the "OSD" button to save the settings.

Hotkey: The "+" on the side of the monitor.

Note: If you encounter a situation where the option for brightness is grayed out and can't be adjusted, please make sure that "HDR" and "DCR" are both "OFF" and "ECO" is set to "STANDARD". Or you can simply click "RESET" in "OSD SETTING".

Then you can try to adjust the brightness again.