I still need to emphasize that I tried 2 types of scanning 1) Advanced scan running on and targeting localhost; 2)Credentialed scan targeting localhost.
If I use a local user in "Administrators" group, to perform a credentialed scan, are changes to Windows security policy still necessary?
But regarding "Advanced scanning" mode:
Are you saying that the LocalSystem account that Nessus uses to run, does not have sufficient privileges to scan the local system? That does not make sense to me. It should work without providing any credentials if you only target localhost. At least this is how I remember from my own experience from years ago.