If we receive a call at an inconvenient moment, we can simply reject or dismiss it by swiping the red decline icon on the Xiaomi smartphone screen.

Android 11 | MIUI 12.0
How to Reject an Incoming call - Drag the  Phone button  downwards
How to Reject an Incoming call - Release the  Phone button  to reject the call
  1. Drag the Phone button downwards
  2. Release the Phone button to reject the call

Xiaomi Instructions