The "Mute all sounds" function can be found in the Listening section of the LG smartphones' Help menu, and when activated, all sounds from the device are muted.

Android 9 | LG UX 9.0
Mute all sounds -  Open the  Settings
Mute all sounds -  Tap on  General
Mute all sounds -  Tap on  Accessibility
Mute all sounds -  Tap on  Hearing
Mute all sounds -  Enable or Disable  Mute all sounds
Mute all sounds -  Confirm with  Turn on
  1. Open the Settings
  2. Tap on General
  3. Tap on Accessibility
  4. Tap on Hearing
  5. Enable or Disable Mute all sounds
  6. Confirm with Turn on

LG Instructions
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