macOS Photos Not Enough Local Storage.

My Mac mini (M1) is unning the latest macOS 15 on Mac Mini, with iCloud 2TB plan.

My mac got 256GB internal SSD and a USB external 1TB SSD.

I got about 306GB photos on the iCloud.

Photos app failed to sync with "Not Enough Local Storage" error while my OS disk still have 126GB space.

The Optimize Mac Storage should allow me to sync the Photos event I don't have enough local storage to store full-resolution library.

When I was running macOS 14, I can delete the photo library and let it sync again from the iCloud, with "Optimize Mac Storage" I can use for a few months before I hit this warning again.

I have moved the library to the external disk already.

I have logged an Apple support case about the, the support told be the message complaints about the System disk instead of the external disk, even I moved the library to external disk. Apple staff told be I have to reserve the same size of free space as the photos on the iCloud, in order to make sync works... I said, it doesn't make sense!! The "Optimize Mac Storage" option should make it works...

If I moved the library to the external disk already, why still measure how much space on the system disk?

I already used "Optimize Mac Storage" option.

I already paid for 2TB plan.

Why still got this kind of error?

It is totally not make sense, the Apple staff agree by point by can't explain why.

I hope macOS 15 fix this problem.

No. Even I removed the library and let it sync again, it complain "Not Enough Local Storage" immediately.

Anyone has a solution?

Thanks!