Incoming calls are displayed on the Oppo smartphone via a full screen by default, and all we have to do to answer a call is drag the green icon upwards.

Android 11 | ColorOS 11.0
Step 1: Drag the  Phone icon  upwards
Step 2: Release the  Phone icon  to answer the call
  1. Drag the Phone icon upwards
  2. Release the Phone icon to answer the call

Oppo Instructions