The TYPENAME and TYPENAMES parameters defined on one of the Name values reported in FeatureType returned by the GetCapabilities request of the Web Feature Service (WFS) must be added to the custom parameters of the WFS ArcGIS Pro connection. Otherwise ArcGIS Pro fails to establish the connection.
Adding TYPENAME or TYPENAMES as a custom request parameter is not required for working with WFS layers in ArcGIS Pro. ArcGIS Pro obtains layer name information by reading the service's GetCapabilities document. Unfortunately, this service is no longer available for testing. If the issue persists, contact Esri Technical Support.