Use "Launch -> Local action" to launch a local action in overlay and inside the overlay configure a repeating dynamic layout with pagelist / data page. The section included in the repeating dynamic layout should hold 2 things,
1) a check box property to capture multiple selection
2) value of the selected item.
How to capture the selection ?
Configure "Post Value" and "Run Activity" actions on the checkbox control. The activity will basically accumulate the selected entries and push the results to multiselect property.
How to refresh the multiselect property ?
Configure the dynamic layout containing this property to "refresh when property changes".