I recently went through this exercise as well - we were migrating to new Windows Server 2022 VMs from 2016 VMs. And although I didn't run into issues joining the portal site, once I removed the old portal machine from the site the federated and hosting server sites would no longer validate.
What I did was go into the SecurityConfig in the ArcGIS Serve Administrator Directory at
....6443/arcgis/admin/security/config
and I could see that for Portal Properties I needed to update the Private Portal URLs:
"privatePortalUrl": "https://OldDNSName.org.net:7443/arcgis",
to
"privatePortalUrl": "https://NewDNSName.org.net:7443/arcgis",
Once I did this, then the federated and hosting sites validated just fine.