I have been working on adding photos to to my photos library. Today, it seems that I have none of the newly added photos or any of my more recent albums. What has happened?

Perhaps you're viewing them in date order? If you copy over photos that were taken earlier, they'll be sorted further down the list. So just scroll down.

Are you looking at the correct Photos lIbrary? You can see the location of your Photos Library, if you open the Photos > Preferences > General. The first line of this panel is showing the path to your current Photos Library. in the line "Library Location".When you click on the name of the library in this panel, a Finder window will open, showing you the library. Perhaps the current library is different one from the library you haven been working with recently. You may have used a library on a connected external volume. Did you have a backup drive connected, where an additional library is stored?

You're welcome. I am glad you could recover your photos 😊