Wait a sec… your post confuses me.
First you’re messing around with a Windows 10 update, creating new users(?!) – and in the end its Plex’ fault?
Never heard of a Win10 update that requires users to be re-created.
As for your server… as expected by Windows, Plex stores certain information in the Windows Registry. If you create a new user and run Plex with that user, it will no longer have access to the settings of the Plex Media Server previously created (using a different user). Therefore it’ll try to create a new one.
That has nothing to do with Plex Pass nor not.
That’s just how apps on Windows are working. If you open Outlook or an alternative fully configured e-mail app from a different Windows User account, it won’t show the e-mails of the other user.
There’s ways to run Plex as a “service” on a Windows setup – this way it won’t be linked to an individual user (well… technically it does – but not one of your “human” Windows users) and can run even if you’re not logged in.
Beyond that… if you want to restore your mess, you’ll need to dig into the registry and clean up some of the Plex Media Server settings there.
The support article linked below is for a different use case but it’ll show you what registry parameters Plex will be looking for
https://support.plex.tv/articles/204281528-why-am-i-locked-out-of-server-settings-and-how-do-i-get-in/
