Delete groups and Smart Groups in Contacts on Mac
If you created groups or Smart Groups, you can delete them at any time. The contacts who are in the group are not deleted from Contacts.
In the Contacts app on your Mac, select the group or Smart Group in the sidebar.
Press the Delete key, then confirm the deletion.
If a group isn’t deleted, it’s probably used in a Smart Group with the condition “Card is member of” or “Card is not member of”. You can’t delete the group until you remove the condition or delete the Smart Group.