Lost photos

GuyserB wrote:

Isn't iCloud Photos is that service where you have to pay a monthly fee to back them up? I don't use that.

After all my maneuvering, the oldest Time Machine version I have is just two weeks old, when the photos were already missing. I've lost those photos forever, haven't I?

iCloud does not back up the photos, it stores them in the cloud and you can access them form there, or download them when you wish to your Mac. That is not a backup, but rather a storage and sync system.

I doubt your photos are lost from your Mac, but your Photos Library may be damaged or corrupted so the Photos app is having trouble accessing them.

Open Photos app, go to Preferences, select General, and note the file that is serving as your Photos Library. The images should be in that Library file, which is actually a special type of folder. Locate the file in the Finder, then right click on it and select Show Package contents. You will see some files and folders listed, select list view, and then under View select Show View Options, check the box to Calculate All Sizes.

Back to the listing of files and folders inside that Photos Library file ... look for a large folder, most likely with the name Originals (or Masters). That large folder (gigabytes in size if there are thousands of images) should have the images you are looking for. Open that folder and open the folders within and you will eventually see the actual image files. If your Photos Library is no longer working properly, e.g. displaying those images properly, you can create a new Photos Library by closing Photos, then reopen it holding down the option key and create a new Photos Library. Then you will have an empty Library. Select File => Import and select that large folder called "Originals" or Masters" to import all those images into your new empty Photos Library.

There is a possibility that you won't find such a large Masters (or Originals) folder in the old Photos Library -- that could occur if you configured Photos to NOT copy images into the Photos Library, but rather to leave them in place wherever they are on your Mac. If you did that and those locations have been changed or renamed, then the pointers to those files won't work. If that has happened, you can still find them by searching your entire Mac for all files with names contains .jpg or .jpeg or .heic and you will see where those image files have been placed or moved to. It will take some time but you can reimport them into a new Photos Library again.

You can restore using the backup you made before upgrading. Restore your Mac from a backup - Apple Support

you can also check iCloud.com/photos to see if your photos are in iCloud. Your device may need to sync fully. Open Photos, select library. At the bottom you’ll see the current iCloud status.

Recover from your TM backup.

iCloud is a synchronization service to keep your files in sync across devices; it’s not a true backup. If you don’t find your photos on Time Machine, they are gone forever.