The volume for media content can be set on the OnePlus smartphone independently of the ringtone volume.

The media volume includes all apps, such as games or streaming services such as YouTube, Netflix & Co.

Note: Received or played WhatsApp voice messages are also included in media.

Android 10 | OxygenOS 10.0
Step 1:  Open the  Settings
Step 2:  Tap on  Sounds & vibration
Step 3:  Swipe  left  or  right  to set the  Media   volume
  1. Open the Settings
  2. Tap on Sounds & vibration
  3. Swipe left or right to set the Media volume

OnePlus Instructions