What is supposed to be the monetary underpinning of cryptocurrency?

it’s not even that useful. IIRC reading that of the mined gold in existence, 50% is sitting in vaults as bullion, 40% is jewelry, and the remaining 10% is used for things like electronics.

whether we want to debate how “useful” jewelry is is up to the board.

It’s useful to signal wealth. So it kind of goes in circles.

Which is why you see Bill Gates and Jeff Bezos so covered in jewelry that can’t even move.