Photos

Good afternoon Navybankie,

Welcome to the Apple Support Communities!

I understand you are having an issue when you open the Photos application on your Mac. The System Photo Library is the iCloud Photos library. It is the one that syncs photos and videos between your Mac and your iPhone. To see which photo libraries you have on your Mac, first quit the Photos app.

Then, press and hold the Option key on your keyboard, and click the Photos app icon on your Dock. You should see a list of libraries. Choose the one that has System Photo Library after it.

Note: The correct library name is usually called Photos Library. It will most likely be the largest library in the list. The name indicated above sounds like some type of temporary file to me. Please reply to this thread if you have any questions when you look at these files.

Designate a System Photo Library in Photos

Set up and use iCloud Photos

Take care.

Hi Matt,

Thanks for letting us know that you were able to get back to your System Photo Library.

In addition to the resources above, I'll include some additional information here to help you the Photos application.

Photos User Guide - macOS Catalina

How to manage photos on your Mac - Apple Support YouTube

Enjoy your day!