Re: "Can't delete Group in Contacts"
Here are a few suggestions to browse through, before choosing one or more for trouble-shooting.
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You could try quitting, and re-opening Contacts, to check whether you can now delete ok.
If not, Quit Contacts, Restart your Mac (Apple menu > Restart) and log back in, Open Contacts and check again.
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Else:
Apple support have an article online that may help:
How to: Delete lists and Smart Lists in Contacts on Mac - Apple Support
says:
"If you created lists or Smart Lists, you can delete them at any time.
The contacts who are in the list aren’t deleted from Contacts.
In the Contacts app on your Mac, select the list or Smart List in the sidebar.
Press the Delete key, then confirm the deletion.
If a list isn’t deleted, it’s probably used in a Smart List with the condition “Card is member of” or “Card is not member of”.
You can’t delete the list until you remove the condition or delete the Smart List".
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More info. / support / contact:
MacBook Pro support website:
MacBook Pro - Official Apple Support