Calling it a "grift" may be harsh, but "Havana syndrome" as a result of some kind of Cuban sonic super-weapon that happens to have the same noise as some local crickets was definitely an enormous stretch. That plenty of people played along with it to the extent that bills were passed allocating funding for the treatment of these people might not be a grift but it's certainly something extremely peculiar. With US healthcare in the state that it is, I get that some people might need to be creative to get treated so I can't exactly blame anyone (nor get mad since I don't pay US taxes).
My guess is more of a mass hysteria situation combined with politicians that are exceptionally credible toward anything the military says than a conscious grifting.