I would suggest to you create a Search helper entity associated with your template grid entity and add an on-change microflow that filters your list and associate the list with the search helper entity and refresh the parent entity of the page.
In your Page, the Template Grid Datasource should be via association.
or
you can use datasource as microflow and filter your list based on the selected list and return the list.
In this case, in your Onchange microflow, u need to refresh the parent entity and that will trigger the ds flow again and return your filtered list.