Are favorites in the Photos app suppose to sync between devices?

I use Apple Photos on my Macs and on my iOS devices. I can flag photos via the Heart icon as favorites, but in my case they are not synced between devices.

Is this a bug, or is this meant to be like this?

ps: I saw the question Are "Favorites" and edits synced with Photos for Mac/iOS?, but it neither attracted answers nor is it it particular current - that's why I ask this here and now.

They will (or should) sync between devices if you are using iCloud Photo Library, otherwise, e.g. when syncing just the PhotoStream, favourites do not sync.

I just tested this on a device running iOS 12.1.3 and macOS Mojave 10.14.3 by favoriting a photo in the iOS photos app, and not only did the photo appear in the Favorites album in Photos.app on Mac, the Favorites album was automatically created in both places. (I don't use Favorites, but they do seem to work for me.)

According to Apple's Support article for iCloud Photo Library, edits do indeed sync between devices. I also confirmed this just now by cropping a photo on my Mac, and watching the cropped photo appear on my iOS device.

NB: if you are trying to sync favorites between devices using a hardline sync such as iTunes, I am unable to describe what the correct behavior for that is, as I don't have a setup to test it with currently, nor could I find any information on Apple's support website.

According to this Support article from 2016 the answer depends on how you sync:

• If you import photos from an iOS device to Photos over USB, the favorite status will not sync (!) but edits should (at least they do now, but not back then, I've tested this)
• If you use iCloud Photo Library to sync across devices the favorite status will sync along with the edits.

Source: Apple Support - Q: iOS Photos to OSX Photos favorites sync

FWIW this is totally offensive and horrible, I can hardly believe it. I just did an import of 3k images and apparently have lost all of my favorite statuses. What a mess.