Hi Karol,
> ... we are wondering when the Dashboards for ArcGIS currently in beta testing for ArcGIS Online will be available for use with Enterprise
I would estimate that the new ArcGIS Dashboards Beta will likely be part of the ArcGIS Enterprise release after 10.8.1. FYI: the Enterprise team is working on 10.8.1 now, and I don't think ArcGIS Dashboards Beta will be finalized in time to be part that release.
Hope this helps,