I'm happy to accept that I was wrong, in fact this is a very interesting bit of technology! I didn't intend to be rude, unlike you, clearly.
I'd also like to add that beamforming, despite the name, does not actually involve creating a directed beam. As I described the antenna still sends a signal out in all directions - multiple antennae work together to create an interference pattern with a stronger signal where a device is located. While I wasn't aware of this technology, it is not as "directed" as the name implies and wouldn't necessarily have applications inside a microwave oven, especially since the wavelengths used are pretty long, so I don't think they would not have much flexibility to create the kind of precise pattern that cooking something while skipping the empty space would require.
Would any of that really make it heat more efficiently though? You'd need at least two magnetrons, some sort of computer vision system, and a computer to do the necessary calculations. Even if you could practically produce an interference pattern that's better than a single standing wave, I suspect you'd lose more energy than you save.