The library “Photos Library” is from a newer version of Photos. Please upgrade Photos to open this library.

Please check, if a System update is available on your Mac. The Mac, where you migrated the library from, ay have had a newer version of Big Sur installed. Update to the same version or a newer version.

Photos for Mac is a part of the system and updated by updating the system. Photos cannot open a Photos Library, that has been opened and modified by a newer version of Photos from a newer system version.