Nothing. It's non-ionizing radiation.
Microwaves ovens work by using extreme amounts of energy concentrated into a very small area.
Microwave beams for energy transmission are different.
We've known this since at least 1996 when the first paper talking about it was published.
https://www.sciencedirect.com/science/article/abs/pii/0038092X95000834
The biggest obstacle for it is actually RFI.
Edit to add, and here's a NASA paper from the 1980s talking about it