Can't unenroll from Apple Beta Program: All System Preferences popups freezes Version: 10.15 Beta (19A526h). 

Behavior:

The window in the picture becomes unresponsive after this popup appears. I can't press "Restore Default" at all. I've restarted my computer, went in terminal and entered sudo softwareupdate --clear-catalog, and then went in the App Store to get the stable release of Catalina. Anyway, it doesn't help because it takes me to System Preferences again, where it becomes unresponsive. 

Is there something else I can do to get the stable version of Catalina on my machine? 

Update: Was able to use keyboard (tab / space / enter) to select "Restore Default", I enter my password when I'm prompted but then the window just closes and nothing changes. Have also tried the same thing with installing Catalina from Mac Store. After downloading ~6GB, it pops up ad says "Update Not Found: The requested version of macOS is not available."
It took multiple attempts to download the Catalina update. The last attempt gave an error, but somehow the install screen for Catalina showed up and I was able to perform the update. The issue with System Preferences seem to have been fixed.