The value of currency comes more from the state enforcing it rather than tangability. It's a bit of a meme by now because of how often I see the book mentioned when money comes up, but "Debt" by Graeber is a good read on the development of money.

Ever since the gold standard was abolished by Bretton Woods agreement, money wasn't really tangibly anything. It used to be "I trust the government has a piece of gold they say is the value on this note stored somewhere". Then it became arbitrary value related to a bunch of central bank stuff that comes down to moving numbers around on a spreadsheet. Now we're moving money more directly on spreadsheets somewhere.

Money becoming more traceable as stuff changes to credit cards and apple pay is a different issue IMO.