This is very much a 'Chi-word' for me (a word I've learned from playing Chi), although I have come across it occasionally in films and TV progs.
I've a feeling I heard it in Frances McDormand's 'sure to win an Oscar' film 'Nomadland'
It's in COD, but written with a capiital (Nimby).
I suppose it should be capitalized, since it is an acronym formed from a direct speech utterance -'Not in my back yard!', although I suspect it may have become transmogrified into a noun or an adjective - '... protests from the nimby community...'
I don't think it should be common, though.