The "Mute all sounds" function completely mutes the Samsung device. all sounds including calls, warnings and media sounds are disabled. when you press the Volume up/down key, the sounds are disabled and marked "Mute all sounds" is on.

Android 10 (One UI 2.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Accessibility
Step 3:  Tap on  Hearing enhancements
Step 4:  Enable or disable  Mute all sounds
  1. Open the Settings
  2. Tap on Accessibility
  3. Tap on Hearing enhancements
  4. Enable or disable Mute all sounds

Samsung Instructions