Expand Enable Adaptive Brightness and set it to Off. In the Power Options dialog, locate the Display entry and expand it.
Under Choose or customize a power plan, click Change plan settings.
Right-click the Start button and click Control Panel. If the screen brightness is not working in Windows 10, you could try to disable the option Adaptive Brightness. Here is a guide on how to fix the brightness control not working problem in Windows 10 (Creators Update/Fall Creators Update 1709), applied to HP, Asus, Dell, Lenovo, Toshiba, Lenovo, MSI, Samsung and other brand PCs. They can't increase or decrease the screen brightness.
Recently, a lot of users reported the brightness not working issue in Windows 10.
