photos is not open with an error message "Photos quit unexpectedly"

A few things to check immediately.

If the library is on an external drive, is it formatted correctly (APFS or MacOS extended (journaled)

Try starting in safe mode - does it work now - if so, restart normally - is it fixed?

Try creating a new library - add a few photos. Does it work in the new library?

Try a new user account - does it work in a new user account?