If an installed app on the OnePlus smartphone no longer runs properly, has operating errors, or cannot be closed, we can force the app to be closed.
The system will close the selected app without regard to possible data loss if the data has not yet been saved properly.

Android 10 | OxygenOS 10.0
Force stop (App) -  Open the  Settings
Force stop (App) -  Tap on  Apps & notifications
Force stop (App) -  Tap on  See all apps
Force stop (App) -  Choose an  app
Force stop (App) -  Tap on  Force stop
Force stop (App) -  Confirm with  OK
  1. Open the Settings
  2. Tap on Apps & notifications
  3. Tap on See all apps
  4. Choose an app
  5. Tap on Force stop
  6. Confirm with OK

OnePlus Instructions