Nick Szabo spelled it out clearly in 2002, and the fact that he spelled it out before bitcoin had been conceived to me gives it a more scientific basis. It was predicted, and then it manifested itself.

Money starts as a collectible. The fact that physical commodities can be collectibles is incidental. Not all commodities become collectibles. For example, during covid oil had negative value. Collectibles don't ever have negative value, they might go close to zero but by definition there is always someone willing to pay more than zero to own and hold them. Houses are collectibles, rare wine if a collectible, gold bullion is a collectible, antique furniture is collectible. It is the fact that it's collectible that gives it value, not that it is a collectible because it's valuable. Air is valuable, but not collectible, because to be a collectible it must be difficult to collect, because the function of a collectible is to discriminate between the people who have it, and the people who don't, because the people who have it must have sacrificed or worked or been clever enough to get it cheap (foresight), in other words to be a collectible a thing must be capable of measuring the capacity and capabilities, the means, the status, the quality, the worth of the owner.

Then from there they can either be SoV or MoE, depending upon the response of the incumbent governance system. In our case bitcoin is a store of value first because of financial suppression and a propaganda campaign, because governments who don't hold bitcoin cannot pay their historical liabilities, and they cannot buy it without pumping the price. If there were no government backlash bitcoin would become a medium of exchange, even marginally so, and then due to its properties it would quickly become the dominant medium of exchange.

And the final stage, once it's the dominant medium of exchange and store of value, is unit of account, the thing by which everyone and everything is measured.

Fiat is no longer a collectible, so it's dying as money.