The OnePlus smartphone's alarm clock can automatically mute itself after a set alarm time, for example to avoid waking the entire neighborhood if it is overheard.

The following options are available for this:

Android 10 | OxygenOS 10.0
Step 1:  Open the  Clock app
Step 2:  Open the  Settings
Step 3:  Tap on  Silence after
Step 4:  Choose an  option
  1. Open the Clock app
  2. Open the Settings
  3. Tap on Silence after
  4. Choose an option

OnePlus Instructions