Context menu of Assign action in Classic UX allows users to see all the list elements already assigned to the selected parent element in one place - the right panel (Screenshot 1). This view is very convenient for many users.
At the same time, in the Assign action menu in NUX already assigned elements are displayed together with all other elements, and there is no option to hide unassigned elements (Screenshot 2). For example, your assigned element can be the last item in a large product hierarchy and you may not notice that it is already assigned before the action is finished. It would be great if a possibility to see only assigned elements is added to the context menu.
As an option, this feature can be implemented as a special filter button which hides all unassigned elements (Screenshot 3). Or an extra tab containing only assigned elements can be added to the Assign action menu as a second step of action before finalizing (Screenshot 4).