IMAC photos updating but not syncing to icloud
I have paid a subscription so all my photos will be on iCloud and available across all my apple equipment
On my MacBook and iphone everything is good they have synced to iCloud and also to the MAC. However on the MAC (which is where I have 60k photos) it just shows constantly as updating and not syncing old photos. If however I add new photos to the MAC then they do get synced to iCloud, MacBook and iPhone. I have tried switching off and back on again, but can’t find a solution. Thanks for any help
iMac 27″, macOS 12.7