where do I find the operating system version I'm running on a MacBook Pro? I need to upgrade to the macOS 10.15 Catalina

Click on the Apple icon on the upper-left side of the macOS menu bar, and then, select "About This Mac."

Yes, I noticed that when I first ran the Reminders app after I upgraded my iPhone to iOS 13. In my case, I elected to not "upgrade" Reminders until Catalina is released in October.