If we want to receive calls while the "Do Not Disturb" mode is active, we have to add them to the exception: On the Oppo smartphone we have the possibility to allow calls from all, from contacts or from selected contacts.

Note: On the Oppo smartphone, a single contact can be marked as a VIP, and this contact is automatically excluded from the "Do Not Disturb" mode.

Android 10 | ColorOS 7.0
Step 1:  Open the  Settings
Step 2:  Tap on  Do not Disturb
Step 3:  Tap on  Allow calls from
Step 4:  Choose between  From anyone,   From contacts only ,  Starred contacts only  and  No one
  1. Open the Settings
  2. Tap on Do not Disturb
  3. Tap on Allow calls from
  4. Choose between From anyone, From contacts onlyStarred contacts only and No one

Oppo Instructions