Photos app stuck at restoring from iCloud

You haven't told us much about your system-- What computer and what OS are you using? Where is your Photos Library located-- in the Pictures folder on your internal drive, or are you using an external drive? With 200K pictures, I suspect that you are using an external drive.

First thing is, how is the external drive (if that's the case) formatted? To avoid damaging the Photos Library an external drive must be formatted in either APFS format or Mac OS Extended (Journaled) format. Additionally, the drive can not have had Time Machine on it since it was formatted. The newest macOSs won't even allow a Library on a non-Mac formatted drive to open since there is a chance of damaging the Photos database. See this:

Move your Photos library to save space on your Mac - Apple Support

Not knowing more, the only other thing to say is that 200K images might be pushing the limits of Photos, and beyond. Most of us who have lots of pictures keep multiple smaller libraries-- especially since some groups of pictures just don't change much. I've got a Library of my wife's old family pictures, and one for my own family's old pictures, for instance. And I have other archival libraries. I've picked the best pictures to put in a Favorites Library that is the one that syncs with iCloud, and I copy new pictures from my iPhone from there to a library of iPictures. Everything works faster.

Hey dirkr--you seem to have a very different sort of situation from the original poster, here. Your best bet is to start your own thread. And when you do, it will help if you read what I said earlier and answer those questions. I mean, for instance, you didn't even tell us if you're talking about a Mac or a phone, so, well, there's not much we can say.

And this is why a stop altogether with Photos in iCloud. I have had it for many years, with a collection growing into 50,000 photos. Mostly it runs well, but if for one reason or another you have to move your photos to another disk, or to do a major reorganisation, it is unpredictable what exactly iCloud will sync and how much time it will take. Think week instead of hour.

Every so often there is a random inconsistency, a photo that does not sync to one of the devices.

So I use photos off line and transfer photos manually from phone to Mac.

My library is just 10 photos. And the syncing hangs for an hour now. While it should be a matter of seconds.

After a bit more waiting time, suddenly iCloud started syncing. I was using an iPhone and a Mac, and both were waiting for iCloud.