iCloud Drive isn’t quite like Google Drive or Dropbox. As with most Apple digital and cloud services, it’s tied to a single identity without much in the way of sharing. iCloud Drive’s sharing features seem a bit tacked on.
Macworld reader Howard writes in asking about an aspect of this. “I was hoping also to have my wife’s iCloud drive show up on my Mac’s Finder the way I do with Dropbox. I haven’t been able to get this to work.”
It’s not you, Howard. You can only mount a given iCloud Drive associated with an iCloud account on an account in macOS logged into that same iCloud account. With some previous Apple cloud storage systems, you could use the credentials (user name and password) to mount a drive without having your system logged into the same account.
You can select individual files in macOS, the iOS app, or via iCloud.com and share them. But access is solely via the web, and you can’t share folders.

Only individual files can be shared in iCloud Drive.
Apple lets you share iCloud storage using Family Sharing, but it doesn’t provide any way to share files among those family members, either. Howard’s family bumped up their storage and has now bumped against this limit.
Dropbox is a very reasonable way to have a shared folder, the contents of which are constantly synced among those connected to the folder. One other option would be to use internet file storage via Panic’s Transmit 5, which allows several kinds of servers and cloud hosts to be mounted as Finder volumes. However, this doesn’t use sync: you’re really opening and saving files live over the internet, which can add lag unless you have a relatively fast broadband connection.
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