Reminders gave you the option to upgrade or not. Upgrading means that you upgraded reminders to a state that will not work with older operating systems. That's why the warning was there about the effects of upgrading. I haven't upgraded my reminders on iPad OS 13 because all my other devices are running current software and not betas. So, my reminders works across all devices.Interesting. So on older iMacs that are not able to use Catalina are you saying I just need to delete my Reminders app, forever?