Fiat currency is called that because it doesn’t have any intrinsic value. It’s backed by confidence alone. The solution usually seems to be “invest in precious metals”.
But it seems to me that precious metals suffer the same problem. It’s simply buried a little further into the woodwork.
Gold has no real function other than decoration, and trading for real goods such as cows and grain.
In that case, backing up fiat currency with another, even more abstract fiat currency seems like a bit of a bad plan. The American dollar should be backed by cows and grain.