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 https://ntrs.nasa.gov/citations/19800010018