I've been trying to move files or folders to online-only for three weeks now, and it never works.
I do NOT see the option to move a particular file to online-only when right-clicking on its name, the command is only accessible via the "Manage hard drive space" menu - but it doesn't work here.
I have two MacBook Pro running macOS High Sierra (10.13.6), and the Dropbox application v203.4.4857.
Thanks in advance!