File action type on file not in Drafts folder?

I’m trying to append text from a draft onto a text file I have in my iCloud Drive not under the Drafts app Folder (/My Docs/lists/domains.txt) that I need to access from other apps. I’ve tried playing around with the path to no avail and the existing action doesn’t use the path, and the documentation seems to indicate you can, but I’m not groking quite how.

File action steps can only write to files inside the Drafts folder. This is an Apple sandbox limitation. Related docs.

You can create files outside that folder using Export actions, but you cannot append/prepend.