Parental controls still enabled under Ventura after using Migration Assistant from an El Capitan machine; Screen Time is off

My son was using an old Mac Mini running El Capitan. Parental Controls were enabled on this machine. Recently I bought him a newer Mac Mini. It's running Ventura. I migrated all his data from his old machine to the new one using the macOS Migration Assistant. This seemed to work really well; he was even still logged in to his Google accounts in Google Chrome. I activated Screen Time via iCloud (or it was active already -- I don't remember -- since it was configured to work across devices via iCloud), but it didn't seem to work properly: When I was trying to configure the machine late one evening it kept on logging out (doing the turning animation to the login screen), and immediately again when I entered the password. Also the machine would start using 100% CPU and basically completely lock up; the mouse would move but nothing else would work. So the next day I disabled Screen Time via iCloud completely, on all his devices. I reactivated Screen Time on his iPhone and iPad without iCloud. Screen Time is still off on the Mac Mini. Since then the machine has been rock stable with no 100% CPU problems. Yet -- remembering that Screen Time is off -- every day at 15mins before 20:30 (the previously configured "end time" under Parental Controls) the warning pops up that the time is almost up. So the previously defined Parental Controls are still active. How can I turn them off?