Restore Photos Library from TimeMachine

Macs can have multiple Libraries, and only the one that's designated as the System Library can connect to iCloud. So if there is already a System Library on your A-Mac, then restoring the Time Machine Library shouldn't change that. And a Library shouldn't get connected to iCloud automatically. Still, I would turn off WiFi, restore, and check the status of the Libraries. There's nothing to lose by doing that. You should think about names of your Libraries so you don't get all mixed up.

Are you planning to have this Library on the internal drive of Mac-A? Are you sure there's room? Connecting a new Library to iCloud doesn't remove what's already in iCloud Photos. You'll get a combination of both Libraries, and that might be larger than you expect. Photos will try to avoid exact duplicates, but you may end up with a bunch of the same pictures with different names, etc.

If this is to be a Desktop Mac, then you can move the Library to a properly formatted external drive. I say desktop, because it's best not to plug and unplug the System Library connected to iCloud, and that's hard with a portable. See this:

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

It would be best to avoid using "Optimize Storage" with your main Photos Library. You should back up this Library, and backing up an Optimized Library doesn't include all the original files.

Let us know if you need clarification…

Jim Jarvie wrote: … Are you saying to delete the iCloud linked libraries from each device, so that all devices have no photos and then iCloud will have no photos and THEN do the restore from Time Machine to Mac?

Yes-- but if they are connected to iCloud, you only have to delete the pictures on one device-- the others will copy. I'd have a copy of that Library on an external drive before doing that, though.

Photos uses the capture date that's in the metadata of the picture file. If that date isn't included with the picture, then it will use the only date it has-- the file creation date. Lots of methods of transferring picture files remove the metadata to avoid privacy issues, especially methods between devices. Email and websites, for instance, often remove metadata. In Photos you can choose to export pictures without personal information.

You should try the Time Machine restore to see if Photos ever had the correct date, but I'd check that out first before making any drastic changes.

I'm afraid you didn't add much clarity. Do you have pictures in iCloud Photos now? If so, they won't go away when you connect a new Library. If you have a picture with Aunt Ethel dated 2035 and you turn on a Library that has the same picture of Aunt Ethel dated 2023, then you'll get both, of course. Photos will not attempt to decide which one to keep.

If you're wanting to replace the pictures in your current iCloud linked Libraries, then you will need to empty those current Libraries before turning on the replacement.