Old reminders are gone from macOS 10.14.6

I'm so confused about what happened to the macOS version of the Reminders app.

Reminders 6.0
macOS Mojave 10.14.6

My mobile version of Reminders has the old data and it seems to work fine. I don't think it is syncing with the desktop version though, because the desktop version is showing, "The creator of this list has upgraded... learn more here, https://support.apple.com/en-us/HT210220..."

All the reminders are gone, with only two lists, Scheduled and Reminders.

The link isn't super helpful, I followed the iCloud link and signed in there, and I can see the list of my reminders in the browser.

So how do I recover in the desktop app?

According to Apple:

To use the new Reminders features in iOS 13—smart lists, a new quick toolbar, and more—you need to upgrade the reminders in your iCloud account.

Upgraded reminders aren't compatible with earlier versions of iOS and macOS. If you upgrade your reminders on your iPhone with iOS 13, your iPad and Mac using the same iCloud account can’t access your reminders until iPadOS and macOS 10.15 Catalina are available.

You will need to wait until you upgrade your Mac to Catalina before Reminders start to sync to your Mac again.