in version 2.0, the GroupByControl was replaced by a HierarchicalGroupByControl by default. If you don’t use the MasterDetail feature, the GroupByControl is used as the ControlTemplate for the HierarchicalGroupByControl in the HierarchicalGroupByControl default style in .
Just set an implicit style on the GroupByControl type in your application.
If it still does not work because other templates were modified, set an implicit style on HierarchicalGroupByControl and set its style to “tableViewHierarchicalGroupByControlOldGroupByControlTemplate” which is located in TableView.GridElementTemplate. This will force the HierarchicalGroupByControl to use the old GroupByControl.