Hi,
In the ArcGIS Maps SDK for Javascript (I'm using v4.30), the PortalItem property "modified" only relates to when the properties of the PortalItem was modified.
I'm displaying a grid of PortalItems which all happen to be Feature Services, and would like to display when the last changes to the feature service itself (attribute change or geometry reshape etc.) was. Doing something like loading each Feature Service would not be ideal due to how many are listed.
If that's not possible, I'm also semi-happy with whatever the ArcGIS online portal uses for the "Item Updated" value, as that doesn't line up with the PortalItem.modified property either.