Android has a better API, and has had it for at least 5 years. An app can open the system UI for you to choose a file, and it would then only get access to that particular file while the activity (screen) that requested it is running. As far as the user is concerned, this requires no permissions. Under the hood, the app gets a content:// URI with an "URI permission" granted. This is also how sharing (Intent.ACTION_SEND) works. You could as well use this mechanism to expose the content in your app to other apps in a controlled manner.

Yep. Android also has a Contact Picker that doesn't require contacts permissions where you just select a single person in a dialog.

I have never seen it used in a real app. Most apps request permission to your entire address book.

iOS does this for photos as of iOS 14: https://www.macrumors.com/2020/06/24/ios-14-users-give-apps-...

I wish there was an easier way to add additional photos quickly. From what I understand the only way is search for the app in settings, open the "Photos" permission and click on "Edit Selected Photos". Is there an easier way I missed? I guess I can't expect a simple click from within the app itself while selecting photos, as it's not aware it's seeing a limited selection.

I think it requires developers to fix that. At least in Slack there's two buttons next to their in-app image picker. One opens the camera to take a photo, the other pops up the iOS photo picker overlay where you can select more images.