Traditional vocal removers (like Audacity’s "Vocal Reduction and Isolation" effect) rely on phase inversion. This only works if the vocals are exactly the same in the left and right channels (mono). FNF vocals are often panned slightly or have reverb effects, meaning phase cancellation will destroy your song’s quality, leaving a "robotic" or "underwater" sound.
Modern AI-powered vocal removers.
Whether you are a fan making a meme remix or a serious mod developer, using a vocal remover for FNF is the only way to get clean instrumentals without contacting the original composer.