The tag is "FN@Fbg". It's not a replacement for describing the background, rather it mostly alters the pallete of the scene to fit a murky FNAF location. This lora was trained on character-free backgrounds from a mix of FNAF 1, 2, 3, SL, and UCN. It was created with Moonbeam.
You may notice that the tag is different than the Anything-v5 Version, this is because the previous tag causes issues with generations. Having a tag that doesn't contain common words in it alleviates this.