What is the files and folders permission?

Hi there, I am currently making an app and trying to download content to a user-selected download directory (like how safari does it).

However, whenever I set the download directory outside the App's documents, I get the following error when running my code on a real iOS device.

downloadedFileMoveFailed(error: Error Domain=NSCocoaErrorDomain Code=513 "“CFNetworkDownload_dlIcno.tmp” couldn’t be moved because you don’t have permission to access “Downloads”." UserInfo={NSSourceFilePathErrorKey=/private/var/mobile/Containers/Data/Application/A24D885A-1306-4CE4-9B15-952AF92B7E6C/tmp/CFNetworkDownload_dlIcno.tmp, NSUserStringVariant=(Move), NSDestinationFilePath=/private/var/mobile/Containers/Shared/AppGroup/E6303CBC-62A3-4206-9C84-E37041894DEC/File Provider Storage/Downloads/100MB.bin, NSFilePath=/private/var/mobile/Containers/Data/Application/A24D885A-1306-4CE4-9B15-952AF92B7E6C/tmp/CFNetworkDownload_dlIcno.tmp, NSUnderlyingError=0x281d045d0 {Error Domain=NSPOSIXErrorDomain Code=1 "Operation not permitted"}}, source: file:///private/var/mobile/Containers/Data/Application/A24D885A-1306-4CE4-9B15-952AF92B7E6C/tmp/CFNetworkDownload_dlIcno.tmp, destination: file:///private/var/mobile/Containers/Shared/AppGroup/E6303CBC-62A3-4206-9C84-E37041894DEC/File%20Provider%20Storage/Downloads/100MB.bin)

The summary of that error is that I don't have permission to access the folder I just granted access to.

Here's my attached code (I'm using AlamoFire since it's easier to understand, but I'm having a problem saving files in iOS):

import SwiftUI
import UniformTypeIdentifiers
import Alamofire

struct ContentView: View {
    @AppStorage("downloadsDirectory") var downloadsDirectory = ""
    
    @State private var showFileImporter = false
    
    var body: some View {
        VStack {
            Button("Set downloads directory") {
                showFileImporter.toggle()
            }
            
            Button("Save to downloads directory") {
                Task {
                    do {
                        let destination: DownloadRequest.Destination = { _, response in
                            let documentsURL = URL(string: downloadsDirectory)!
                            let suggestedName = response.suggestedFilename ?? "unknown"

                            let fileURL = documentsURL.appendingPathComponent(suggestedName)

                            return (fileURL, [.removePreviousFile, .createIntermediateDirectories])
                        }

                        let _ = try await AF.download(URL(string: "https://i.imgur.com/zaVQDFJ.png")!, to: destination).serializingDownloadedFileURL().value
                    } catch {
                        print("Downloading error!: \(error)")
                    }
                }
            }
        }
        .fileImporter(isPresented: $showFileImporter, allowedContentTypes: [UTType.folder]) { result in
            switch result {
            case .success(let url):
                downloadsDirectory = url.absoluteString
            case .failure(let error):
                print("Download picker error: \(error)")
            }
        }
    }
}

To reproduce (Run on a REAL iOS device!):

1. Click the Set downloads directory button to On my iPhone
2. Click the Save to downloads directory button
3. Error occurs

Upon further investigation, I found that safari uses the Files and Folders privacy permission (Located in Settings > Privacy > Files and folders on an iPhone) to access folders outside the app sandbox (see the attached image for a visual representation of what I'm talking about). I scoured the web as much as I can and I couldn't find any documentation for this exact permission.

I have seen non-apple apps (such as VLC) use this permission, but I cannot figure out how it's granted. I tried enabling the following plist properties, but none of them work (because I later realized these are for macOS only)

<key>NSDocumentsFolderUsageDescription</key>
<string>App wants to access your documents folder</string>
<key>NSDownloadsFolderUsageDescription</key>
<string>App wants to access your downloads folder</string>

Can someone please help me figure out how to grant the files and folder permission and explain what it does? I would really appreciate the help.

Image of the permission in question: