Above, I said it already says "AllowRootLogin=true".
I copied and pasted that text right from the file.
However, I went back and looked at the file again after posting that, and then it was set to false!
I have no explanation.
However, I did edit it to true, and now I can log in via the KDE log in as root.
However, once I am in as root, if I try to end the session and log back in as a user, it will not log in and returns me to the KDE log in.
If I log in via console as a user, then launch KDE, I am back in as the user.
It seems the added self-protection has made the changing user process more cumbersome. In fact my recollection is that the older version had a choice when ending the session, to relaunch as a new user. I no longer have a choice. Only button on the end session splash screen is to end current session.
Anyway, I can do what I want to do, it is just more of an effort than it used to be.