Ethnostate is an ambiguous word. Does it mean ethnically homogenous? Israel is certainly not that. Does it mean, essentially, a nation-state whose "national group" is an ethnicity? Israel is that - but so is much of Europe and some parts of Asia.
Edit: I asked ChatGPT "How many nations have declared themselves to be the Nation-State of a people?" earlier and got the same answer as you. I asked again just now and got "Israel is the only nation in the world that has legally declared itself the “Nation‑State of the Jewish People.”" [I didn't specify Jewish]
