Keep in mind, this does not work in Jerboa. It will open a browser tab trying to go to https:///c/some_community@server.tld.
Also, if nobody in your instance has ever subscribed to that community, it results in a 404 error.
EDIT: Nobody should be subscribed to this dead-end sub created and abandoned: Link. Should result in a 404 error for everyone not from sh.itjust.works.