Best backup sorting for photos

If you are using Photos for Mac, the Time Machine backup of your Mac can include the Photos Library and you can recover the current version or older versions of your Photos Library from Time Machine.

This will work and suffice as a backup, provided the originals of your photos are stored locally on your Mac.

• If you are using iCloud Photos and "optimise Mac Storage" to save storage on your Mac, the original image files may only be in iCloud and you need to save them separately by downloading them from iCloud. Or keep a not optimised version of your iCloud Photos Library on an external drive, as described here: How to back up an optimized iCloud Photos Library - Apple Community
• The originals may also be missing from the library, if you did not copy them into the library on import, but are referencing them in the original location. Then you need to include the location, where the originals are store,d in your Time Machine backup.

Another complication, If you are running macOS 10.15 Catalina or newer is, that Photos is no longer storing the originals with the original filename, but renaming them. We can no longer extract the original image files with the original filename from a Photos Library, if we cannot run Photos. We need to run Photos on a Mac with the same system version that has been used when saving the library (or a newer system version) installed to recover the original image files from the Photos Library. This is usually no problem, if we keep our Mac running the current system version, and the Photos Library does not get damages, and Photos is working well. It will be a problem, however, if we have to downgrade the Mac to an older system version, or if the Photos Library gets damaged, or Photos will not run, for whatever reasons. Or if we should decide to switch from a Mac to a different brand of computers.

I would prepare for such an emergency and make a separate backup of the original image files by exporting them from Photos to folders named like the Moments.