I just recently upgraded my Test & Development ArcGIS Enterprise from 10.8 to 10.8.1. I ran into an issue configuring Portal web adaptor in Development environment with "initial administrator account" username and password as I didn't have an issue with Test environment, see attached image. Portal machine and Portal for ArcGIS services were running. So when I access https://portalmachine.domain:7443/arcgis on the portal machine with initial administrator account username and password, I couldn't get in. I could only log in with my own username & password.
Contacted ESRI Support and found out that I must have "initial administrator account" as a Creator/Administrator on my Portal in order to configure Portal Web Adaptor. I did remove initial administrator account for Dev & Production environment to free up the name users account for other user as per ESRI documentation, About the initial administrator account, "The initial administrator account user name and password are stored by Portal for ArcGIS. The initial administrator is not an operating system account, and has no relation to the Portal for ArcGIS account. Later, you can specify other accounts as administrators, demote the initial administrator to a role with fewer privileges, or delete the initial administrator if you choose." If initial administrator account is required to configure Portal's web adaptor starting from 10.8.1, should ESRI changes the documentation that initial administrator account should not be deleted? If this is new, why did ESRI changed for the 10.8.1, it's taking a name user account and doesn't make much sense to me.