Small correction - iCloud Photos are only end-to-end encrypted if you enable Advanced Data Protection, which was introduced in December 2022, and otherwise Apple has the keys. See https://support.apple.com/en-us/102651 for more details.

So the uploaded photos in question couldn’t have been e2ee. Even so, it’s reasonable for people to question the legitimacy of e2ee given instances where it’s been shown to be a lie or for the data to also have been transmitted without e2ee, like Anker’s Eufy cameras’ “e2ee” feeds clearly being accessible without keys from the user devices, or WhatsApp exposing tons of messaging metadata to Meta.

That said, I personally wasn’t using iCloud Photos prior to enabling Advanced Data Protection, and I had a few deleted photos show up from several years ago, so Apple’s explanation makes sense to me. And, like you’ve pointed out, most of the speculation was devoid of any critical thinking.

Well people had other people's photos popping up in their own photos app. So not sure how they handle 'encryption'. But it's best to treat all photos uploaded to cloud as public, because that's likely how it is. Can't trust Google, Amazon or Apple with your data when they can and are making so much money off of it.

As its all proprietary you can’t, and basically nobody can, say anything about a backdoor. It’s pure trust in this corporation.