The photo library could not be opened error (3142). Anyone know how to get it back?

Where is your Photos Library stored?

Photos 8 on macOS Ventura is much more particular about the location of the Photos Library. It should be in the Pictures folder on your Mac. If you keep the Photos Library on an external volume, prepare the external volume as described here: Move your Photos library to save space on your Mac - Apple Support

The external volume needs have a compatible file system format, also it needs a wired connection (not a NAS!), and it should not have been used for Time Machine backups or have any backup software installed.

If the library is already in a compatible location, the library might have become damaged. Photos should have tried to repair it. If that did not hapen, make a backup copy of the library (but do not overwrite an older backup, you may need it!) and repair the library ( Repair the library ). If all fails, restire the library from your backup: Restore from Time Machine

What has happened, before you could no longer open the library? This error message istypical for libraries, that have been damaged by aggressive cleaning softwareor keeping the library in a synced folder, for example a Dropbox.