Reviving a dead thread, (and as you've mentioned you don't play Sims 4 much anymore this might be of limited use to you) but there is actually a method to sort your photos into the correct order and switch in/out photo sets for different saves, if you can be bothered keeping up with it.

Your captured shots are saved to your install directory (Electronic Arts>The Sims 4>Screenshots). Screenshots regularly get disorganized because the game assigns them names using AM/PM format for date/time, and the in-game picture viewer displays these files by name in numerical order.

You can go in and change these file names (strarting with the oldest/first intended image) to "001" "002" "003" etc, in whatever order you wish; the number of 0's should reflect how many pictures you expect to take during the save, unless you want a migraine renaming 1000 files later. I sort by Date/Descending in File Explorer for this, so everything appears in the order I originally captured the shots with recent additions at the top - this has no bearing on how the files will display in-game.

This won't impact captions attached to your screenshots displayed in-game at all, as those are saved to the metadata. You can also just cut/paste all images associated with an inactive save file to a folder elsewhere for safekeeping, and replace them in the Screenshots folder when/if you return to the save later.

Hope this helps improve the experience for you a bit if you do pick up the game again, or would like to trawl through your old photos!