Currently, ArcGIS Online has the function to export the hosted feature service data to CSV or SHP. However, Portal for ArcGIS does not have this function.
The workaround seems to be using ArcMap and connecting to the service or connecting directoy to the managed database and export the data and it's only the users who have access to ArcGIS for Desktop and not all Portal for ArcGIS users have access to the Desktop.
There are some cases users want to export the data to CSV and use it with Excel or other ways.
So, I'd like this Export to CSV/SHP fuction to be implemented in Portal for ArcGIS.
See the help: Exporting to CSV