I'm unable to find where this question has been answered but the new JiraCloud release does not render links to attachments according to the documentation. When I enter [^attachment.txt], it shows up as that rather than creating a link.
Toggling to the older view reveals my text was converted to \[^attachment.txt]
I tried changing the renderer to the "Default renderer" but my text shows up as [^attachment.txt] with no link and no apparent way to fix it.