Created groups can be easily removed from the Xiaomi device. Only the group without contacts is deleted, leaving them on the device.

Android 10 (MIUI 12.0)
Step 1:  Open the  Contacts app
Step 2:  Tap on  My groups
Step 3:  Tap and hold a  group
Step 4:  Tap on  Delete
Step 5:  Tap on  OK
  1. Open the Contacts app
  2. Tap on My groups
  3. Tap and hold a group
  4. Tap on Delete
  5. Tap on OK

Xiaomi Instructions