Photos app not syncing with iCloud

photosbynick wrote:

I have 450k photos in my photos app on my Mac mini m2. I have 263k photos on my iPhone 16 pro. I have both devices set to sync to cloud to optimize storage. Photos have not synced between the two devices since before December 2024. I tried opening photos app on my MacBook Pro m1 and it only shows 233k photos. All 3 devices are signed in to the same iCloud account and iCloud Photos is turned on. I tried to chat with Apple but they do not seem to even understand where to begin. Hopefully someone here has had the same issue before and knows how to fix this. Also note, all devices are updated to the latest public version too.

Photos doesn't "sync" between a Mac and an iPhone-- iPhone Photos syncs with Photos at iCloud.com, and iCloud syncs with Mac Photos. So--What do you see at Photos at iCloud.com? Is iCloud synchronized with either device?

What does the Mac say at the bottom of the Library? Like this:

What does the iPhone say in the Apple ID icon at the top of the Photos app?

Are you sure all three Libraries are signed in to the same Apple ID?

Off topic: The Mac mini really should not be using Optimize Storage, even if you have to attach an external drive to hold the Library. You can't back up your Photos collection otherwise.