Is the heat used by cooking something actually used up?

Factual Questions
21

This will vary DRAMATICALLY with the drag coefficient of the car. The more aerodynamic the vehicle, the more the disruption is going to affect the fuel economy. A pickup truck will have a much lower impact of having windows rolled down than a small sports sedan will. And you’re just pulling numbers out of your rear at this point.

In the early 2000s, I drove a Dodge Intrepid 30 miles to work each day. On the days I could stand it, I used the 4/65 cooling method – 4 windows down, 65mph – and it was notably more efficient by a few MPG than running the AC

22

As noted upthread the era of the vehicle matters too.

Lots of old mumble's tales from 1960s cars are still repeated as current gospel by listicle authors and their AI bots.

If the cite / site doesn’t say which model year vehicle(s) they gathered dat from, good bet your just reading freshly copied Olde Tyme lore.