Hi, @Qbit Global Admin
Based on your description, I understand that you are experiencing an error message associated with your account when deleting a group folder.
1.Check again if the account in the EAC was successfully removed.
2.Can you see the group folder in OWA?
Here are some steps you can try.
1.In Outlook, click the File tab in the top left corner.
2.Click on Account Settings and then select Account Settings from the drop-down menu.
3.If you want to remove the folder, make sure that it's not set as the default file. If it is, you'll need to set another file as the default first.
4.Select the file, and click Remove if you no longer need it.
5.Close the Account Settings window and restart Outlook to see if the issue is resolved.
If that doesn't work, you can still try removing full access to the mailbox.
You can use command
Add-MailboxPermission -Identity <shared mailbox alias> -User <your mailbox alias> -AccessRights FullAccess -InheritanceType All -Automapping $false