I know. All backed by what? Nothing. Other than a group of like minded people believing it’s worth something... because.
All currency is backed by “nothing” except the imputed value of people who decide it is reliable as a means of exchange. The utilitarian value of gold is less than 1/10 of its market value were it not an acceptable means of exchange. There is no such thing as “instrinsic value” in currency.
The worse part of this is of course that the people never decided to accept pictures of paper with dead politicians on them. That was a “fiat” decision by the state. In the long run, anything that challenges this fiat will do well.