Cheers Ben Turrell Ill try my best.
Hi Sam Maloney
Please find Owen Evans comment on Copy online story map to on-prem portal. His comment was "Unfortunately copying a StoryMaps item to your portal won't work since the code for the new ArcGIS StoryMaps doesn't exist in your portal environment. We're looking at bringing the new StoryMaps to ArcGIS Enterprise and will have more to announce about that in 2020.".
I hope this has answered your question.