Photos stay on the phone
The short version
Mavaul is a vault for photos and videos. They stay on your iPhone, encrypted with AES-256. There is no account. We don't have a cloud, and we can't open your vault.
The free app holds 20 photos and videos. Premium removes the cap, and adds encrypted backup, crop, extra home screen icons, and email recovery.
What it is not
It is not a hidden folder inside Photos. The Hidden album still lives in the Photos library. Mavaul is a separate app with its own passcode.
If you want the files somewhere else, Premium can write an encrypted backup to Dropbox, Nextcloud, or Files. That copy is encrypted on the phone before it uploads. We don't host it.