You can’t copy/paste from a Read Only project, so you need to create a clone, even if you aren’t planning to use the cloned project.
Then it’s just a matter of copying the elements under Body one by one, from one project to another (you can’t copy the entire “body” of a page at once) - making sure the structure stays the same. Bit cumbersome if the page has a lot of separate sections.
Usually, you’ll need to check if there’s any custom code that needs to be copied too (though the example you mention doesn’t have any).
I think you can run into some trouble if existing classes in your project are the same as in the cloned project, can’t recall how well Webflow does at renaming those without interfering with interactions.