By duplicate items, did you mean to have duplicate records or to move multiple items at once? Maybe you are looking for a button that will transfer the one or more selected items from one grid to another?
1. Having duplicate records depends on whether the database you update when you add a row to a Grid allows that.
2. Moving multiple items at once is possible and can be tested in the demos you shared below. Select more than one item, then drag it to the Grid on the right.
3. Moving items is done visually, but once they are dropped at the destination, only the information in the items are moved over, the Grid will render the element once refreshed. So, you can try to implement a button which if clicked, will loop through the selected items of one Grid, get their record IDs, copy these records from Grid1 dataSource to Grid2 datasource and finally remove them from Grid1 datasource.
Here is one useful article I would recommend for this case: Accessing Cells and Rows
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