Admins if this is in the wrong place please move to the appropriate place.
If you have configured a single machine install of Portal/Server/ArcGIS Pro and find that ArcGIS Pro will not allow you to add the local portal link (https://FQDN/portal/) and or log into the local portal check your IIS configuration for port 443 bindings.
We had a situation where the server IP was plugged into the site bindings instead of the default [ All Assigned ].
We spent many hours going through logs and configuration settings before someone noticed the issue in IIS.
Once the setting was changed to All Unassigned everything worked as it should.