So what happens if it’s miniaturized and connected in series by the millions?
It's basically an antenna, so miniaturizing it will reduce the amount of RF it's exposed to and consequently how much it can capture. If you miniaturize it and connect enough of them together in series, you'll eventually get the same amount of power as a big one.
You'll get millions of micro watts. That will be enough to power a couple of night lights. Electromagnetic energy in the air must come from near by emitting sources. It looses efficiency at the cube of the distance from the source. Only a tiny fraction of it is harvestable. It is about the least efficient way of transmitting power imaginable.