Display of Group Footer

You can specify whether to display group footers during row grouping using createFooterCallback().
If you return true, the Group Footer will be displayed, if you return false, it will not be displayed. (default false)

This is an example of not displaying when there is only one data row belonging to a group.
You can create the desired condition values by referring to groupModel.

Scroll to the bottom of the grid and see that no group footer has been created.

   gridView.setRowGroup({
     mergeMode: true;
     expandedAdornments: "footer",
     createFooterCallback: function(grid, groupModel) {
       if (groupModel.descendantCount > 1) return true
     }
   })