How Do I Duplicate a Project - with assignments/tasks/date intact - but make it not visible (back-up purposes)

My team is piloting a new workflow and wants to use a duplicate of their existing project. They want to retain a copy of the existing project as back up if they wish to revert to the old workflow (including all cards intact). Is there a way to do this? If I duplicate the board it appears to drop all dates/assignments etc. The duplicate tasks also appear searchable. Could I duplicate and archive somehow so the cards do not appear as duplicates via search? Or is there an export/import solution? Thanks in advance!

The duplication window has a lot of options to choose what is duplicated.

And then you can make it a private project just to you. Would that work in your case?