I think what you’re looking for would be to do with UIDocumentPickerViewController, but I’m not certain.
Also, Apple includes two code-level support requests per year as part of the Apple Developer program. Have y’all reached out to them for code-level support here? It might not be something super easy to do on the JS side of the app, but it should be possible.
I’m not an iOS developer anymore, but I’ve done iOS before. I still have an app in the Mac app store, and last year I had to reach out to Apple’s code-level support folks for an Xcode filesystem related issue and they were super helpful. It took them a few round-trips to understand what I was having a hard time with, but we got there and they were super helpful.