Some users have noticed settings that let Meta analyze and retain phone photos

IMO Apple should provide the user with audit logs of which photos/videos were accessed by each app. It might be a long list but it alleviates doubt and would put huge pressure on reputable developers to ensure they don’t get caught doing things the user wouldn’t have expected (even if the user technically allowed it).

I don’t understand why apps need access to my photos at all. (with some very specific exceptions,) apps should only access a photo, which I first select using the system photo picker. There’s no need for apps to access the entire camera roll just so I can select one photo to use with that app.

I know that that’s partially implemented with the limited photo access now, but it’s confusing from a UI perspective and I don’t understand why this isn’t the default.

The only apps that need full access to my camera roll, are apps like Google Photos, Nextcloud or Immich. Everyone else can suck a lemon.

I saw the canon camera app now needs full access to photos.

It used to just need to add to it.

this means - an external camera that wants to just add photos to the photo roll needs full access to all photos.

By "needs" I take it that you mean "is programmed in such a way to require" and not that the permissions are required to do the job you are asking of it?