Moved Photos Library to External SSD, now corrupted

I am keeping many libraries on external drives, but the volume needs to be compatible with Photos:

Where is the Photos Library stored, that cannot be repaired?

A common reason for not be being able to open a library is keeping a library on an external volume with an incompatible file system format. Before try to repair the library, make sure it is on an compatible volume as described here: Move your Photos library to save space on your Mac - Apple Support

If you try to repair a library on an incompatible volume, you may make the damage worse.

Any external volume you are using with Photos needs to be prepared like this:

• The file system format needs to be MacOS Extended(Journaled) of APFS
• The external volume must not have been used for Time Machine backups or have any backup software installed.
• It must not be mounted on the local network but use a wired connection. Do not even think about putting the library onto a NAS.
• The library must not be in a synced folder like a Dropbox or on Google Drive or similar
• As a test: if you cannot set the Ignore Ownership on this Volume Flag, the external volume is not suitable.

Even if you could use the library with earlier versions of Photos, there may have problems all along. Photos 8 on Ventura is checking the location of a library more thoroughly than earlier version to prevent damage.

And you cannot share a library between two different user accounts, unless you set the "Ignore Ownership on this volume" flag.

To repair a Photos Library see: Repair your library in Photos on Mac – Apple Support (UK)

I have moved .photoslibrary files to external discs on several different Mac systems, and not always successfully. I learned the hard way, make backups first!

Any chance that the external drive where you moved the problematic .photoslibrary file was then connected to a newer version of macOS, and thus, a newer version of Photos than the macOS and Photos versions you're trying to use now?

A newer version of Photos apparently automatically updates the .photoslibrary file to the newest version of Photos connected, and once that happens, that .photoslibrary file can never be opened by older versions of Photos.

If you discover that the 'newer Photos version' problem caused the issue, you should be able to successfully open the photoslibrary file with that newer version.

The 'Repair database' has never helped me recover from this issue.

The two ways I've found to recover from the problem:

1) Restore from a backup created before the problem happened;

or

2a) Using the newer Photos version, Export everything as individual files.

2b) Create a new empty .photoslibrary file in the older Photos version, and

2c) Re-import everything back into the older Photos version.

Hope this helps!