The screen belongs to the no. 1 battery consumer, so the brightness also plays a major role in how long the battery lasts. On Samsung devices, the brightness can be adjusted either manually or automatically to suit the lighting conditions. For manual adjustment, the adaptive brightness can be turned on, but it is always overwritten.

Note: The brightness can also be changed manually using the quick settings.

Android 10 (One UI 2.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Display
Step 3:  Move Slider to adjust  brightness
  1. Open the Settings
  2. Tap on Display
  3. Move Slider to adjust brightness

Samsung Instructions