my installation is with only one ArcGIS Server (Hosted)
the upgrade went great for all components
WebAdaptor (Portal) ok
ArcGIS Portal (ok)
WebAdaptor (Server) ko (impossibile registration)
ArcGIS Server (ok)
ArcGIS Datastore (ok)
after the upgrade I realized that I had not cleaned / uninstalled the following applications,
ArcGIS Insight 2021.1.1 Help Language Pack
ArcGIS Insight 2021.1.1
ArcGIS Excalibur 2.2
ArcGIS WorkFlow Manager Server 10.9
ArcGIS WorkFlow Manager 10.9 Web App
after a snapshot restore, I am now uninstalling the "AddON" applications before performing the upgrade.