Allow saving photos to the Photo Library

Feature request

Is your feature request related to a problem? Please describe.
I have been using Nextcloud with the auto upload functionality, thinking that this would serve well as a way to backup my phones Photo library without having to pay for iCloud+

However, I have now experienced the process of actually attempting to restore from Nextcloud, and have discovered that it is a massive pain and I eventually had to give up the restore and borrow a Mac.

Describe the solution you'd like
The app should support saving large amount of photos to the photo library.

Please don't suggest just viewing the photos in the Nextcloud app because that photo viewer is:

1. Far behind the iOS photo app in terms of features
2. all other apps integrate with the native photo library for share features, not Nextcloud.
3. Kind of unstable with larger amounts of photos anyway

Describe alternatives you've considered
A commonly suggested "solution" is to select items in the Nextcloud app and using the iOS Share API to save the items in the photo library. However this very quickly breaks down with even a moderate amount of pictures. Attempting to save even 2000 pictures, which is only about 5GB of data, the Nextcloud app will just hang for several minutes until it eventually crashes. It simply seems that the iOS share API is not designed to handle hundreds or thousands of files.

The only working alternative so far seems to be to either pay for iCloud+ or have access to a Mac computer.

Additional context
The only realistic solution that I see is to add the functionality to asynchronously save large batches of photos in the background. I know that Apple likes to put down arbitrary limitations sometimes, but as far as I understand an app with full access to the photo library shouldn't have any issues saving photos one-by-one(?)

What would be really nice is if there was a feature to "reverse" the Auto Upload to do a "one-click" import of all the photos in the auto upload destination.

The issue names no files, tests, or entry points. Start by locating the iOS app's existing Auto Upload, photo-library access, and share-flow implementations, then clarify background behavior, permissions, batch limits, and completion criteria; done means reliably importing large photo batches without the current hang or crash.