Photos Library

Have you checked, if your external volume is suitable for a Photos Library? YOur external drive should be prepared as described here:

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

Most important:

• The file system format needs to be MacOS Extended (Journaled) or APFS (for an SSD drive) - "formatted for Mac" does not suffice for libraries, only for single files.
• The external volume must not have been used for Time Machine backups or have any third-prty backup software installed
• The drive needs to have a wired connection and not been accessed over the local network. Don't even think about putting the library on a NAS.
• If you cannot enable the "Ignore ownership on this volume", your external drive is not compatible.

Have you checked it? Previous system versions may not have been giving an error message, if the file system format has not been supported. macOS Ventura is more critical will no longer open a library on a volume, where the library could get damaged.

Is the file system format of the volume APFS, not case-sensitive?

Can you set the "Ignore ownership on this volume"flag in the Info for the volume?

If the external drive is an SSD, it would be better to format it APFS. For another type of hard disk MacOS extended (Journaled) should suffice. But try to open a copy on another drive.