Hmm, yeah, that is interesting. I’d say every native German knows “nix” (as in nothing). Maybe 10% would be aware what a “Nixe” is (female water spirit).

Personally, I wasn’t even aware that there’s a male version. I could’ve guessed what it means, when used in a sentence, but if you asked me without context, I probably would’ve been too thick to figure it out. 🙃