iCloud no longer syncing with MacOS High Sierra

I can’t seem to add a contact from my Mac (High Sierra v.10.13.6) to my iPhone 11 (iOS 13.1.2), is iCloud no longer compatible with the old Mac OS? If so, that doesn’t make sense to me because my Notes app seems to sync just fine. Any and all help is much appreciated.

Apple has made no changes here AFAIK. I have had iCloud sync be very slow to see new data created on an iOS 13 device, though. Reboot everything and see if it’s better.