[Solved] Could not estimate size of “Photos Library.photoslibrary”. iCloud Photos will not be enabled.

[Andy]

Suppose you already have iCloud enabled on another iPhone/iPad or macOS, and now you want to enable iCloud Photos on your Mac, and you get this error message:

Could not estimate size of “Photos Library.photoslibrary”. iCloud Photos will not be enabled.

Here's how to solve it:

Launch the Photos app, and then click on the menu bar: Photos -> Preferences... -> General.
Enable iCloud Photo Library in this panel, and make sure Use as System Photo Library is already enabled as well.

The option Use as System Photo Library should be grayed out.

Now we should be able to enable iCloud Photos (tick on the iCloud Photos), you can select Optimise Storage.

Now we have iCloud Photos enabled on your Mac.

Tested on: macOS Big Sur, version 11.5 (20G71)
If you have any questions or comments, you're more than welcome to post them down below

 

[r1389f918fh9138f84g]

Thanks for sharing your solution but it's not even allowing us to click on "settings" (preferences in your case).

We just get this and nothing else.

Photos cannot find the System Photo Library named “Photos Library.photoslibrary”

 

[Andy]

Ah, got it — that means the Photos app can’t locate your main library file. Try this: quit Photos, then hold Option while reopening it. Select your correct Photos Library (or create a new one), then go to Photos → Settings → General and set it as System Photo Library. After that, iCloud Photos should work.

 

[r1389f918fh9138f84g]

Ah, got it — that means the Photos app can’t locate your main library file. Try this: quit Photos, then hold Option while reopening it. Select your correct Photos Library (or create a new one), then go to Photos → Settings → General and set it as System Photo Library. After that, iCloud Photos should work.

Hey Andy, super thanks for your hint, I actually figured out it by myself the last couple of days and managed to do it. But your hint is super accurate, it's exactly what I've done to fix it.

 

[Andy]

@r1389f918fh9138f84g: No worries at all! Glad you got it sorted — nice work figuring it out!