What happened to my photos after upgrading system to Ventura 13.2?

Is it possible that you're connected to the wrong library? Look in your Pictures folder to see if you have more than one Library. If you find another one, double click on it to load it into Photos.

If you don't find another library in the Pictures folder, you can try using the Finder search to locate the others you may have, like this:

If that doesn't work, get back to us with a bit more information. For instance, how are your Settings set?

In Photos>Settings>General,

Is "Use as System Photo Library" grayed out (indicating it is) or solid (indicating this isn't your system library)?

Is "Copy Item to the Photos Library" checked? (This is the default, indicating a "Managed Library")

In Photos>Preferences>iCloud

Is "iCloud Photos" checked?

If it is, is "Optimize Mac Storage" check?

Nearly every app on my computer is acting like it is not connected to any previous use.

I wonder if you created a new user account somehow in the upgrade process?

GO to HD/Users and see how many usernames there are there,