Thanks for your post.
I would like to confirm that whether your supervisor cannot delete one specific file or all the files in the document connection? If just one specific file , then could you please provide a screenshot with the error message? If it’s the latter, please check his permission level in SharePoint Online to see whether he has the permission to delete files.
For your second question, unfortunately, there is no offline function with MAC.
I think more and more functions will be supported in the future. You can also send feedback to our product team via the following link.
http://g.microsoftonline.com/0BX11EN/135
Thanks,
Elaine Hao