It should be caused by too bright ambient light. The easiest way to judge is to cover the screen with your hand and try again with your camera.

If you want to turn on the keyboard light regardless of the ambient light, you can uncheck "Adjust the brightness of the keyboard when the light is weak" by the following steps.

Um ... . It was not until I answered the phone that I found out that your photo was Windows. . . There is no dual system to test at hand. You can only look for BootCamp in the system tray area in the lower right corner of the screen to see if there are any similar settings. . .