With headphones, the sound is usually reproduced in stereo. This means that the sound is reproduced on two different audio channels, with each audio track being heard on one auricle at a time, giving a complete picture only in our ears.

For example, if we share headphones or are deaf in one ear, the Samsung device can switch from stereo to mono audio, and mono audio means that only one audio channel is played, so the output is the same in each ear.

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  Mono audio
  1. Open the Settings
  2. Tap on Accessibility
  3. Tap on Hearing enhancements
  4. Enable or disable Mono audio

Samsung Instructions