What does "Qty" mean on an options trade?

Units of the structure, not contracts. Three iron condors is 3, not 12.

The leg quantities are per unit of the structure, and the Qty field multiplies the whole thing. The builder says it in place: "Qty is per unit of the structure — a 1:2 ratio is 1 and 2, and 3× of the whole thing is the Qty field above."

So a 1:2 ratio spread has legs of 1 and 2, and if you traded three of them, Qty is 3. Counting contracts here instead would inflate your position size everywhere it is used, including your risk pages.