Can a government "back" currency by deeming it to be valuable, without offering to exchange it for a store of value? If not, saying that Bitcoin is "not even b

Can a government "back" currency by deeming it to be valuable, without offering to exchange it for a store of value? If not, saying that Bitcoin is "not even backed" by fiat is meaningless. If so, we are using "backed" in the wrong sense.