Actions are run on a specific draft. Usually this is the draft currently loaded in the editor, if you running the action by tapping on it in the action list.
Action steps like the clipboard step will operate on that draft.
I’m not sure how you are getting “a specific note by UUID”, but if that is in a script, or URL, etc., that does not affect the draft that is in context for the action.
So your clipboard step is probably working, but not getting the result you expect because it’s putting the draft that was in the editor when you ran the action into the clipboard (which is maybe blank).
@jsamlarose’s script above should accomplish what you want in a single script step.