I know, my point is that it is not directly backed by gold, but indirectly you can make the point there astronomical gold reserve comes into play if gold prices go insanely high.
The US GDP in 2024 was 30+ trillion. A single trillion in gold (8133t) is not an astronomical amount of gold, even though it's more than any other owner. In fact, all the gold ever mined is only ~220000 tonnes, so US GDP is higher than all the gold above ground at $4000/oz troy.