Create a selection object and associate it to the object from your data grid. Then pass the selected list from your grid into a microflow, in that microflow associate the list to your selection object that you then pass to your page. In the page, show a nested data grid(list objects) within a dataview of your selection object over the association SelectionObject to OriginalDataGridObject
If the items have an attribute that changes when they're selected (i.e. a boolean that changes to yes on selection) then page 2 could have an attribute constraint where visibility depends on the Selection attribute having a value of "true"