Pictures library empty after WindowServer quit (MacBook Air - Sonoma 16.6.1)

A Photos Library is usually kept in the Pictures folder for a user. Only that User has access to it. Each user gets their own Photos Library that is available only to them. The Administrator account has no access to any personal User accounts. When you opened Photos in the Administrator account, it created a new Photos Library for it, if there wasn't one already available.

If a Photos Library is in a folder that is in the general Users folder, then it can be accessed by any user.

If you close Photos and option-click on the Photos icon, it will bring up a Library Chooser dialog

and I can see that one of my Libraries is in the Users folder rather than in my user's folder. This will be available to all users. Each user has a "Public" folder, but users will need to be approved, I think. There may be some messing with permissions as Libraries are moved around.

The point here is that there can be several Photos Libraries, you may not be seeing the one you though. The Library Chooser shows the last one you used in that account.

Is this what's going on?

OK-- so this is the Library that's available in your own User's account. I'm guessing that if you choose this Library you see your pictures as you expect. It shows this to be the System Library, and it's in you Pictures folder.

What do you see if you do the do the same thing on the Administrator's account?

The name doesn't tell you much, because the default name for every Library is always "Photos Library.photoslibrary." But it will show a path to the Administrator's Pictures folder.

If you want the Library that's in your Pictures folder to be available to all the users, then you should rename it something clever, and put it directly iin the main Users folder. The Europe Library I showed before

Is in the main Users folder, so it's available to all users on this machine.

If you move it, you can open it from your name account with a double click. You may want to make it your System Library-- the library that is used by other apps like Mail and Safari. You do that by going to Photos' Settings>General

You can see the path, here, and you should check "Use as System Photos Library" so that it becomes grayed out.

Let us know if this is working for you…

The first thing you should do is get an external HDD like the OWC Mercury Elite Pro that's about 2 ½ times the size of your boot drive and start using Time Machine. Without it you'll undoubtedly have another issue like this one. It's excellent insurance against data loss.

I'm glad you found your Library! Keep in mind that "Photos Library.photoslibrary" is not a unique name, and every user can have one, so it can be very confusing. The library at "Users/USER#1/Pictuers/Photos Library.photoslibrary" is available only to USER#1, while a library at "Users/Photos Library.photoslibrary" is available to everyone. A library at "Users/USER#1/Documents/Photos Library.photoslibrary" is also available only to USER#1.

I would think that the Library that was in Documents should show up in you own user's Library Chooser.