I am trying to configure a dashobard in our own Portal with ArcGIS Enterprise 10.6.1 but I have found differences between our Portal and an Esri account.
I need to configure a serial chart with the sum of values added in categories and limit the result to 5 columns, but this option does not appear in our Portal if I select "Grouped Values". It only appears if I select "Features".
The release of Operations Dashboard in ArcGIS Enterprise 10.6.1 is slightly "behind" the Operations Dashboard release in ArcGIS Online. Hence why you may see more functionality in ArcGIS Online than in ArcGIS Enterprise.
Hope this helps,