This could be a workaround:
Add a boolean to the entity and call it 'distinct' for example. Then make a microflow to check whether the name for the Case Items is distinct when you add a new object and set the boolean accordingly.
Then you can add an xpath on the datagrid with this newly created boolean, so you only see the objects with distinct names.
You have to base the Grid on the Case entity. You can create a search filter based on a referenced field, in your case the CaseItem entity.
Add a dateselector and in the connector choose the case/case_caseItem/caseItem/Date