If this function is activated on the Huawei smartphone, the channels are connected during audio playback, which means that the left and right speakers reproduce the same content.

Android 10 | EMUI 10.0
Mono audio -  Open the  settings
Mono audio -  Tap on  Accessibility features
Mono audio -  Tap on  Accessibility 
Mono audio -  Activate or deactivate  Mono audio
  1. Open the settings
  2. Tap on Accessibility features
  3. Tap on Accessibility 
  4. Activate or deactivate Mono audio

Huawei Instructions