Photo iCloud download stopped working.

Did you just install an update? Did Photos for Mac have to update an older version of your Photos Library after update or repair it after a crash?

On Sequoia I have occasionally seen the message "Restoring from iCloud" for my Photos Library, when I tried to open Photos after installing a system update and the update of the library format to the system version it never succeeded.

In that case it helped to start over with a new, empty Photos Library. This avoided the "Restoring" step.

If you are sure, that all your photos are in iCloud Photos (you may want to check this in the Photos.app at www.icloud.com ), try this:

• Quit Photos, if it is runnig.
• Copy your current, damaged Photos Library as a safety copy to an external drive.
• Then laugh Photos again, while holding down the options key ⌥ and keep holding down the key, until you are seeing the dialog to select a library.
• Select to create a new library on your system drive.
• When Photos opens an empty library window, open the Photos > Preferences (or Settings) > General and click "Use as System Photos Library"
• Click the iCloud tab and enable iCloud Photos.
• Now wait for your Photos to come back from iCloud.

I have not seen this "restoring" message on Tahoe or Golden Gate, only on Sequoia. Perhaps upgrading will fix it. But I would not upgrade with a broken Photos Library. Downloading a fresh copy from iCloud is the best way to repair a library, when the built-in "repair Library" tool gets stuck because of damaged media in the Photos Library. This is workin, because the new download from iCloud does not include any files that are not compatible with iCloud. Older, incompatible items are not in iCloud and can no longer block the analysis and rebuilding of the library.

I'm not sure what you mean by "I’m trying to download photos from iCloud." Are you using Safari to download images from Photos at iCloud.com? Can you download a single image? Do you see all your pictures at iCloud.com?

Or are you doing something in Photos? Can you tell us

1. Do you have more than one Photos Library?
2. Where does your Mac's Photos Library reside-- in the Pictures folder of your internal drive, or on an external drive? or on a network? on iCloud drive?
3. Do you have “Optimize Storage” checked in Photos’ Settings
4. Have you checked to see if the Apple Account is really really the same on the Mac and at iCloud.com?
5. What is your storage at iCloud.com? At System Settings>[name]>iCloud>Storage , my Mac says 176 GB of 200 GB used. What does yours say?
6. What is your storage on this Mac? At System Settings>General> Storage, my Mac says 745 GB of 1TBB used. What does yours say?
7. What does your Library say at the bottom of the Library view? Like this:

Also, do you use a "VPN?" Do you use Mac "Cleaner" apps? Do you use "Virus catcher" apps?

To narrow things down, try these steps:

1. Restart the computer (of course)
2. Re-start in Safe Mode. This bypasses certain potentially disruptive processes, and it often helps. Safe Mode is different for different computers, so see this: 

           Start up your Mac in safe mode - Apple Support