The brightness of the display of your Huawei smartphone can be changed either over the status bar, or over the settings.

Note: The display is one of the top 3 if you talk about battery drainage. If you set your display on 100%, your battery will be drained fastly. For the best battery usage, you can activate automatic brightness.

Android 10 | EMUI 10.0
Display brightness -  Open the  settings
Display brightness -  Tap on  Display & brightness
Display brightness -  Push the bar to the  left  or  right
  1. Open the settings
  2. Tap on Display & brightness
  3. Push the bar to the left or right

Huawei Instructions