Microwaves absorbed in tissue induce electrical currents carried by ions in solution. Just about everything that happens in your body involves ions moving in solution, one way or another. Details matter.
That will be surprising to those of us who, you know, exist.
Try to use microwaves to move ions from one side of a container of salt solution to the other and then get back to me on the ability of microwaves to control ion movement. Hint: you basically can't without obscene levels of radiation. The thermal "pressure" due to the diffusion of ions is enormous.
For a sense of scale, the thermal velocity of water molecules at room temperature is about 500m/s. The drift velocity(average movement of charge carriers, i.e. coherent current) of typical electric currents is on the order of 1mm/s.
On top of rectification and resonance, the signal would need to be carried in a place where its current has a persistent effect, and the nature of the signal itself, the modulation, would need to be such as to drive some cellular-scale electrochemical process. It is not possible to predict what that would be for the signal in question, if indeed there are any.
We appear to have got lucky with previous generations, but that tells us nothing about the next.
Now, 6B ions is hardly any, in the grand scheme of things, but they are in a very small space, and another 6B are moving in the next channel over. The only places we know of (well, that I know of) where these nanoamp currents are important is in organizing healing, and in embryo development. Old people have a hard enough time mustering healing activity without anything disrupting the process. I don't know what other processes might involve such currents.
Again, we don't know whether 5G modulation will affect healing in old people, but it is certainly physically possible that it can. It will be very hard to measure, but that doesn't mean the physiological effect must be small.
If there is an effect, will we notice? Is anybody monitoring healing rates in old people, at the population level, today? How do you even measure that?