We can set the Navigation Buttons to be automatically disabled when we use certain apps on the Xiaomi smartphone. This feature is useful when you're playing games in full screen, for example, and don't want to accidentally tap a button. You can customize apps here.

Note: To reactivate the navigation key, we have to tap it twice.

Android 10 | MIUI 12.0
Step 1:  Open the  Settings
Step 2:  Tap on  Additional settings
Step 3:  Tap on  Button shortcuts
Step 4:  Tap on  Automatically disable navigation buttons
Step 5:  Choose an  app
Step 6:  Choose  Ask to disable ,  Always disable  or  Never disable
  1. Open the Settings
  2. Tap on Additional settings
  3. Tap on Button shortcuts
  4. Tap on Automatically disable navigation buttons
  5. Choose an app
  6. Choose Ask to disable, Always disable or Never disable

Xiaomi Instructions