In Mojave, Photos has stopped synchronizing with iCloud in any direction. Apple's support is over. Even when opening the iCloud Preferences panel and looking at the Photos sync settings, the Preferences became a beach ball for an indefinite time or for 15-20 minutes, since God knows what. All other photo clients (MacOS and iOS) are synchronized as expected and the synchronization of other iCloud applications on this mac seems functional. The problem is limited to the iCloud synchronization of this Mojave Mac.
I'm throwing a hailstorm here because AppleCare has led nowheresville.
In November, on this same machine, I imported about 60K photos, which I then realized that 30K were thumbnails of the existing phots or other duplicate garbage. In December I used a data and photo removal tool (Gemini 2) that deleted these photos and the deletion was successfully propagated in iCloud. However, since it was completed, all other photo synchronizations have ceased on this client. You are stuck in a state where you think you are waiting to synchronize or start synchronization and it does not progress.
If I can disconnect from iCloud and manually delete the residues that may cause this problem to persist, it would be a great thing to try. If in doing so, the photos merge the database so that duplicates are created, you may prefer to delete the photo database locally and download everything from scratch, as long as you can be sure that the configuration was permanently cleaned, by what the problem will be removed after all my problems
Any guidance on how to deepen the synchronization problems of Photos-iCloud is very much appreciated.