I don’t understand where you believe I am wrong; I said the gold, diamond and bitcoin all have the property that they cannot be manufactured on demand.
Corn can be, and regularly is; iron is abundant. Both are priced by their functionality (with a price floor set by the cost of manufacturing/extracting/growing if we ignore subsidies for a moment). If they become too expensive, they will be replaced by other cheap metals or crop in most uses.
Gold/bitcoins/diamonds just become more desirable when their price goes up.