I don't see photos on my macOS (macOS Big Sur) Photos app but on my iPhone (iOS 14.4) there is info that all photos were "Updated Just Now".
The count of photos in the iOS app is higher than the macOS Photos app.
I've checked the free space on macOS (there is 12GB free space), also iCloud has free space (14 GB free of 50 GB)
Other services like Calendar and Notes sync without any problem with iPhone