Thank you so much for that suggestion. I’d quickly tried it earlier and thought I couldn’t select a folder in Shortcuts. I was wrong: ‘select multiple’ allow selection of a single folder.
So an easy Shortcut allows me to create a zip in the Shortcuts icloud folder.
The only part I would love to streamline is to not have to select the folder at all - I’m always archiving the same iA Writer folder (I was hoping Scriptable could work from a hard coded path to the folder, but it needs bookmark support to do that)