I just deployed ArcGIS Enterprise 11.4 on a client server machine but I am unable to connect the ArcGIS Pro to the portal URL. It gave an error code: unable to establish connection with the portal URL.
Try opening the same link on the web browser of that computer with ArcGIS Pro installed, if you are able to access the Portal URL via the browser then it should open in ArcGIS Pro as well. Option 1 - you might need to check if the URL is correct in structure as per ArcGIS pro requirement. Option 2 - check if any Network Ports might be blocked.
I am able to access the portal URL from the server machine and from another computer on the same network. The URL is well structured.