Apple basically already has this built into macos - you can create an encrypted ...

		UniverseHacker 7 months ago \| parent \| context \| favorite \| on: U.K. orders Apple to let it spy on users’ encrypte... Apple basically already has this built into macos - you can create an encrypted disk image and mount it to access the files. I'm not sure if it is possible to open these on ios.

iOS cannot mount .dmg files (at least, not without jailbreaking).