Support to GeoRSS
Supported GeoRSS formats. Map Viewer follows GeoRSS.org standards for encoding GeoRSS—Simple and GML.
GeoRSS-Simple—Supports point, line, box, polygon, and circle
GeoRSS GML—Supports point, line, box, and polygon
More information about support to GeoRSS here: https://enterprise.arcgis.com/en/portal/latest/use/georss.htm