It's proprietary but that's exactly what Samsung's "Secure Folder" is. Apps, contacts, files, photos ... That can't be listed or accessed without a secondary auth, protected by knox. I don't know about non samsung android phones.
It's fairly simple to use, and if you sometime give your phone to other people / kids / etc ... It quickly becomes absolutely necessary.
Need to remember to use the "secure folder" camera though, if you merely take the pic THEN move to secure folder, while it's super quick and easy it's usually too late as google photos, dropbox, whatever else will already have duped it.
