Automatic brightness fits the brightness of your Huawei device's display automatically to the lighting conditions of your surroundings. You can still adjust the brightness manually if needed. 

Android 10 (EMUI 10.0)
Step 1:  Open the  settings
Step 2:  Tap on  Display & brightness
Step 3:  Activate or deactivate  Automatic 
  1. Open the settings
  2. Tap on Display & brightness
  3. Activate or deactivate Automatic 

Huawei Instructions