Photos

Are you sure you have lost them. Is it possible you are now opening a different library without your images?

Try holding down the option key while starting photos. It should list all the libraries on your system - does one of them hold your photos?

If you keep a Time Machine backup you can restore your Photos library from there.

Otherwise, unless you have some other backup system, you probably have lost your photos. There may be some recovery software that you can find that will recover your photos.

-- Rich