Photosync can automatically move photos from iDevices into consolidated NAS, SFTP, cloud or iXpand USB storage, https://photosync-app.com

GoodReader has optional app-level file encryption with a password that is not stored in the iOS keychain. In theory, those encrypted files should be opaque to device backups or local filesystem scanning, unless iOS or malware harvests the key from runtime memory, https://goodreader.com/