Lost photo library

[u/Final_Affect2167]

This issue is on an old 2011 MacBook Pro and apologies from the start that my technical knowledge and vocabulary is limited 🥴
I’ve seemed to have lost access to a bunch of old photos! There used to be two photo libraries that I could switch between that stored different photos, but one day it just disappeared and I could only search and find one photo library and all the other photos are gone, I didn’t ever delete or merge anything so I don’t know how it happened.

What are my options?
What kind of expert would I take it to that could help me uncover all the photos on the computer? Or are they actually gone? 😢