Unable to duplicate iMovie project on iPhone due to export failure

I can’t seem to duplicate my iMovie project on my iPhone. Long press on thumbnail doesn’t give an option to duplicate. I thought to export/import, but exporting fails (when I choose ‘save to files’ it says ‘not enough space on the device’ while I have plenty of space - tried saving on iCloud and on device). It is a long movie (30 min). Ideas?

[Re-Titled by Moderator]

Original Title: Duplicate iMovie project