Running 15.3.1, I used option PHOTOS and updated one library that appeared. Now I can only find 5 libraries that I apparently unintentionally created over 20 years ago. My system library seems to have vanished'
iMac 21.5″, macOS 15.3
Launch Photos with the Option key held down and see if the missing library appears in the Choose Library window. If it's not there as the System Photos Library see if any of the libraries shown in that window are the right size for you missing library. Open it and see if it's the correct library. If it is you can set it to be the System Photos Library.
If you still can't find your library go back in time in Time Machine to just before you updated the library and restore the library to your Pictures folder.
Launch Photos with the Option key held down and see if the missing library appears in the Choose Library window. If it's not there as the System Photos Library see if any of the libraries shown in that window are the right size for you missing library. Open it and see if it's the correct library. If it is you can set it to be the System Photos Library.
If you still can't find your library go back in time in Time Machine to just before you updated the library and restore the library to your Pictures folder.
Cannot find original photo library on my iMac. My laptop, iBook and phone still access it.
