There are also large benefits in making it harder for Washington to spy on Beijing. I saw a news report 15 years ago or so saying that the Kremlin went back to using mechanical typewriters out of worry that Western intelligence agencies can exfiltrate data from the Kremlin's computers.
That is far, far most likely an RF signal used to power espionage devices. Both the US and the USSR played with putting passively powered espionage devices. The idea it was done to injure embassy staff at this point is a conspiracy theory.
It's not meaningful to call a hypothesis a "conspiracy theory" in this everyday sense when the world of espionage is concerned. Many things that people would intuitively put into conspiracy theory territory have occurred or are even common in clandestine service scenarios. Bugs have been put into buildings during construction years before they were used, radioactive substances were used to track people, one-time pads written by secretaries on typewriters were broken in deciphering efforts that took many years, hardware devices were intercepted and modified during ordinary mail order process, Swiss companies specialized in encryption were entirely compromised and run by the CIA, people have been murdered with poison pellets from a gun looking like an umbrella, etc.
It is a conspiracy theory because the CIA spent 20 years trying to find any effects on health and failed, because medical research spent 50 years trying to find a way how non-heating, non-ionizing radiation could have ill effects on health, and because RF fields to power passive spy devices has been demonstrated many times. Anyone believing at this point that a microwave signal weaker than the leakage of a microwave oven was design to hurt people at the embassy is at the level of a conspiracy theory.
There is no scientific basis for the theory, there are decades of research failing to find either a theoretical or empirical basis, while there are other plausible and precedented hypotheses. Every single example you provided however, was immediately technically plausible at the very least. So yes, the theory it was somehow detrimental to the health of the embassy staff is essentially a conspiracy theory. There is nothing behind it beyond motivated reasoning.
There is an old electric station near me that is used for various things sometimes. Some band was in there shooting a music video and bumped something and somehow the whole area started filling with water. Nobody could stop it.
The government, the water company, everyone was struggling to figure out what to do, and they decided to call the old guy that used to work there. He was in his 90s but he told them how to fix everything.
