I'm trying to free up some room on my hard drive and store it on iCloud as online-only.
According to the following answer, there is a 'remove download' option when right-clicking on any iCloud files / folders in Finder:
Folder in iCloud that stores files only in cloud but doesn't sync with Mac
I can't see this option when I right-click, see attached screengrab at the bottom.
Bear in mind I'm running Mojave 10.14.6 — is this a new feature in iCloud?