I have this issue ArcGIS for Desktop Cannot Connect Portal With Active Directory Sign In
Portal 10.7 with web adaptor recently configured to allow for SAML in our organization.
Through ArcMap, ArcAdmin and trying to license named users in ArcPro, this is the response.
"The URL specified does not appear to have a running portal for ArcGIS"
None of the workarounds work for me. I've added all the associated ports for inbound/outbound from my laptop to our Portal Host. Can ping, etc.