In order not to miss any calls, we can set the ringtone volume on the OnePlus smartphone ourselves.
Note that this setting also affects the volume of the notification or alert tones for new messages, WhatsApp averaging, and system-related messages.

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

OnePlus Instructions