You’re contradicting yourself. You said all value is subjective, meaning it’s derived from nothing but my subjective analysis. You also pointed out that gold has been money for thousands of years… but during those years it didn’t fill cavities, there were no electron microscopes, and no one used electricity. For most of those years it was a shiny rock. Material use cannot explain why they valued it.

The value of fiat no longer derived from gold. It is entirely subjective, like the value of every other commodity (which you correctly pointed out). The subjective valuation for most people is something like “I can buy food with this and also the government is strong and powerful and they say this is the money to use and I owe them a cut denominated in it so it’s the most practical money for me to deal in”. However, it loses value annually, so everyone who accumulates even modest amounts of it begins acquiring other assets as savings vehicles, of which gold is merely one. Others include bonds, stocks, and real estate. There is widespread agreement over what the best unit of account and medium of exchange are, but totaschizophrenia/tribalism over the best store of value. An entire industry has sprung up to help you “diversify”.

Again, “money” only has value because of the expectation that someone will give you something for it in the future. Your choice of money is subjective, and everyone is free to use one form for spending, another for saving, and even a third for accounting. And today they do.

Any of these uses of money is a bet on the subjective evaluations of other people. Thus, money’s value is both your own subjective evaluation as well as your subjective evaluation of others’ subjective evaluations.

One thing I haven’t mentioned too is that doing accounting with gold is an onerous process. Accounting with fiat is much easier. But accounting with Bitcoin is by far the easiest. Accounting innovations have arguably launched our species the furthest of any technology innovations - from single entry accounting and coinage in the cradle of civilization to double entry accounting and banking in the Renaissance.

Even Blockbuster outcompeted the mom and pop video shops because its computer accounting system permitted it to track and remit shared profits to the studios, something that was not possible with pen and paper.

In other words, a return to gold coins from an accounting perspective is so onerous and costly that I cannot imagine anyone doing it