Is it possible to effect peoples health/ nervous system using radio waves or electromagnetic field in some way? I have heard of the "Havana Syndrome" and I was wondering if this could be possible on a smaller scale.
Absolutely. A person could bypass switches in a microwave and run it with the door open facing a neighbor which would be awful. The likelihood of this is next to zero unless you really upset a neighbor who has some technical know how.
If you have a radio tower in your immediate vicinity it could potentially cause issues, depending upon the power output, especially over time.
I remember hearing a couple ham operators chit chatting about modulating radar signals with voice and directing the signal at people driving in their vehicles down a road. Those inside the vehicle would hear the demodulated voices inside their head. They commented on this being back in the 60s before it was known radar signals could cause cancer. The things people do...
Some state higher frequency radio signals (above 1 GHz or so) knock electrons out of molecules in our body. I have not studied this too much however I imagine this is a possibility.
For the most part, radio waves/electromagnetic radiation passes harmlessly through our body.