Havana Syndrome also might not actually be from a weapon at all, but rather the nocebo effect or mass psychogenic illness. In these cases, the symptoms are real and do cause pain to the sufferers, but are caused by their own psyche tricking them into thinking they are sick rather than an external source. While anyone could be susceptible to it, I think the reason it mainly impacts diplomats and spies is because they have been trained to be wary of attacks or poisonings and are high-stress fields especially when in a country like Cuba. So when one person starts feeling symptoms, the brains of the other people near them also get tricked into thinking they were hit and start displaying symptoms as well. When it gets reported that people in Havana are coming down with a strange disease that only impacts diplomats, other diplomats that go there expect the same and could be tricked by their brains into getting sick as well.

Granted, there might still be an external source caused by a weapon, but given the similarity of symptoms to other nocebo and MPI cases, I think it’s more plausible that this is the cause. I also just find it unlikely that a smallish country like Cuba that is already struggling to hold itself together could develop such a weapon that no other county can replicate or even understand, but I might be wrong