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
Automatic brightness -  Open the  settings
Automatic brightness -  Tap on  Display & brightness
Automatic brightness -  Activate or deactivate  Automatic 
  1. Open the settings
  2. Tap on Display & brightness
  3. Activate or deactivate Automatic 

Huawei Instructions