Copy elements from one project to another in Premiere Rush

Not that I am aware of, but you can have more than one timeline (sequence) in a single project, so that you can use the same material in a different edit or version of an edit, adding additional source material as needed - does that help?

If you want to make a difference version of a timeline (sequence) you can find the sequence in Project Assets drawer and, clicking on the row of dots next to its name, choose duplicate from the drop down menu.

Now you will have two independent sequences to work with.

MtD