Can I copy backlog items?

Yes, you can use copy & paste to copy backlog items, in the Backlog page. To do this, select one or more backlog items, and use the right-click menu or Ctrl + C / Cmd + C to copy the backlog items. Then move to where you want to place the new backlog items, select a backlog item there, and paste the new backlog items.

Note that pasting of backlog items is not yet possible in other pages than the Backlog page. In other pages, you can copy (so that you can paste into a spreadsheet, for example), but not yet paste.