PortalUri Property (ArcGISPortal)
ArcGISPortalManager: Get the Current Active Portal
var active_portal = ArcGISPortalManager.Current.GetActivePortal();
string uri = active_portal.PortalUri.ToString();
ArcGISPortalManager: Get a list of all your Portals
var portals = ArcGISPortalManager.Current.GetPortals();
//Make a list of all the Uris
var portalUris = portals.Select(p => p.PortalUri.ToString()).ToList();
Target Platforms: Windows 11, Windows 10
ArcGIS Pro version: 3 or higher.