Others have already mentioned that this is possible with iOS. iOS 14 introduced a bunch of privacy improvements including the PHPickerViewController, but some apps may not yet be using it. [0]

I will say that in the event that an app is not using PHPickerViewController, sometimes it's still possible to emulate it by exiting the app, going into the photos app, selecting the photo, selecting the little "send" arrow in the bottom left, and then picking the app to send it to. I do this all the time with the Slack app. Copy-and-paste may be another route. Sure, it's a silly workaround for a feature that should have been there from day one, but c'est la vie.

[0] https://developer.apple.com/documentation/photokit/deliverin...

> I click “add photo”, the system dialog opens, I select a photo, and then that gets sent to the app. Somehow, Apple managed to screw that up.

That’s exactly how it works for me in iOS at the moment.

In addition, I can see the list of photos each app has been granted access to in Settings > Privacy & Security > Photos.

Exactly this exists. (It’s called PHPickerViewController). It does not require permissions because the image upload process is explicitly choosing an asset.

Photo centric apps may choose more extensive APIs, but those require OS-level permissions (the user explicitly giving access)

Could what you're saying also be basically, you see your whole photos, your whole gallery but the app itself only has access to the one picture you tap on? That way for the user it looks the same as if the app had access to your whole photos, but the app actually only sees the one you select?