A cool project that responds to or takes account of this (trying to make a storage artifact that someone plausibly could learn to use without most of our techno

A cool project that responds to or takes account of this (trying to make a storage artifact that someone plausibly could learn to use without most of our technological knowledge) is https://rosettaproject.org/ https://rosettaproject.org/. It's a somewhat high-density archival storage medium that tries to give a clear hint of what it contains and how to read it, just requiring optical magnification. Of course, that means its overall capacity is many orders of magnitude less than the hard drive you describe.