Now that iOS support mass-storage devices, it should be possible to open and play files directly from outside the sandbox. UIDocumentPickerViewController already supports this mode, and an app developer doesn’t have to do a lot to support this mode (“basically” skip the import phase). On iOS 13, I think the OS even smart enough to restore apps with their file permissions intact so that a previously opened document can also be reopened seamlessly.
In either case, probably should use UIDocumentPickerViewController rather than the deprecated UIDocumentMenuViewController, especially if modern Infuse versions require iOS 12 and up.