Can't access App Store account information

As of 1/24/25, Apple has indeed made changes that lock out older versions of App Store as well as those apps that make use of on-device receipt validation. See here for more info:

TN3138: Handling App Store receipt signing certificate changes | Apple Developer Documentation

They've been rolling this out slowly but steadily, and now the time has come for those of us who rely on older apps and systems to feel the pain. Time marches on and I suppose this counts as "progress", but it's going to hurt a lot of people. So far this affects only one app for me. It's a crucially important app, but I have workarounds and will continue to use my old system. When you purchased that app with a "perpetual" license, Apple has now unilaterally rendered that contract null and void. The developers, if they are still around, won't be issuing an update. Why would they?

[Edited by Moderator]

Update: signing out of App Store then signing back in failed with the same "unexpected error". Signing out of iCloud and back in automatically signed in to App Store. This allows viewing of purchases, but not access to App Store account information, which is necessary to run certain apps purchased via App Store. When selecting Store/View My Account a Console error indicates that for the process "kernel" "loginwindow is not entitled". This occurs before a password is entered. It appears to be something to do with the login window function only. Everything else works.

I also have a 2020 MacBook Air and everything works as expected. I have read many posts on this topic, here and elsewhere, many offering "solutions", none of which work for me. I've seen screenshots of this happening with up to date systems, so it would seem that it's not due to simply running an older system. My first thought was that Apple must have changed something behind the scenes, but now I'm not sure. One additional clue: signing out of App Store and signing back in did not work. In fact, I was not able to sign back in unless I was first signed in to Apple ID. With that, I can sign in to App Store, but still can't access App Store account information. One more additional clue: I have an app, purchased via App Store, that now won't run unless I sign in using the email address and password that was used when originally purchased, which is not possible since those creds have long ago been changed for security reasons. I'll continue to hack away and will post if successful.