The Huawei device suggests, which app have not been optimized for full-screen mode. You can still activate the function and set the setting for each of these apps individually.

Android 10 | EMUI 10.0
Step 1:  Open the  settings
Step 2:  Tap on  Display & brightness
Step 3:  Tap on  More display settings
Step 4:  Tap on  Full-Screen Display
Step 5:  Activate or deactivate the  app
  1. Open the settings
  2. Tap on Display & brightness
  3. Tap on More display settings
  4. Tap on Full-Screen Display
  5. Activate or deactivate the app

Huawei Instructions