Gold does not have to be backed by a commodity, because it is a commodity.
I don't agree that it's useless.
I don't agree that perception is reality. Reality is what is is. regardless of what people believe it is.
So what will happen to gold price when suddenly everyone stop perceiving it as valuable? What if no one buys it as an investment or store of value and the price is solely dictated only by its practical usage (such as electronic and aerospace components)? Will it remain 10% of its current value?
The fact is that most of the gold's price is created by the general agreement that it is precious and valuable, so the 90% (out of the ass estimate) is backed only by perception.
So everyone over night stops seeing a pretty thing as pretty? That would need a cultural revolution the world over Few substances have the color of gold with tarnish-resistence.
https://www.fourmilab.ch/documents/golden_glow/Gold's inate properties make it desirable amongst a periodic table of silvery and dull metal colored elements. That perception of worth is very difficult to remove, unlike the perceived value of e.g. Tulip bulbs, where many people in the day were commenting "but why does it carry such worth when the Rose has much more beauty and variety?"