(A basic law in Israel is roughly like a constitutional amendment in the US.)
https://en.wikipedia.org/wiki/Basic_Law%3A_Israel_as_the_Nat...
I ran the question by AI, and it seems to think that somewhere between 30-50 since WWII have done so explicitly.
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]
Can't rely on AI.