Some groups do not appear to be deletable when you click on the group and then the Action button in the upper right corner of the oc screen.
'Delete Group' is greyed out.
Release : 20.x and 20.4.x
The article is informational
The un-deletable groups are Automatically Created Groups.
To delete these groups -
1. In the operator console, go to "Settings"
2. In the system and administration section, click on "configure"
3. Then de-select the group you would like to remove and save the changes
4. Now the Automatically Created Groups will have 0 elements
They can now be deleted manually using the 'Action' button in the upper right corner - Delete Group