The shortcut, when configured per my instructions, with a single click, will work with a document already opened in Pages, or without Pages running at all. In the latter case, it will launch Pages which should present its template chooser, and after a couple of seconds, a File chooser window will open where you select the Pages document, and then respond to the list of formats. Pages then exports the document in that format and opens a new Mail compose window with that document attached.
The fact that your clicking on the Shortcut resulting in nothing happens suggests to me that something is not correct in the Shortcut. Are you on macOS Ventura 13.0.1?
Launch the Shortcuts application. Locate your Pages shortcut and right-click on it. Choose Edit. Compare what you have in your AppleScript code in that Shortcut to what I posted above for the Shortcuts AppleScript in the finished Shortcut. Anything obvious?