Is there a reason why guest/external users of SharePoint Online cannot use the Copy To / Move To functionality in document libraries that they have permissions on?
(e.g. is it licensing related or a known bug)
SharePoint Stack Exchange is a question and answer site for SharePoint enthusiasts. It only takes a minute to sign up.Sign up to join this community
Per my test in my SharePoint online environment, I share the site to the external user with Edit permission. And then the external user can use Copy To/Move to functionality.
To troubleshoot the issue, you could check the permission of the external user in the document libraries.
And then you could grant more permission for the external user in the document libraries.