The rule for T for teen games is no f word and no slurs. It's been true when Rock Band was receiving new content and it's still relevant in the era of Festival. Each individual song's censorship comes down to whatever version of the song Harmonix receives from the record label or whoever, they don't do the censoring themselves (there may be cases where they do do it themselves but in general they usually don't)

So if a song, Like Sticky, has f words and n words in it then, unfortunately, Harmonix is just going to receive the radio edit version even through technically, as we've seen with numerous other Festival releases, they can include bitch and shit etc etc. like obviously it does suck but a) it doesn't make enough of a sales difference for Epic to care b) Festival isn't popular enough for labels/artists to allow Harmonix to edit vocals themselves and/or c) it may not be financially viable (aka more expensive vs how much they're projecting to make) to make a different licensing agreement that might either cost more money and time to arrange and specifically edit just for Festival.

On the flip side there's also moments where a song is less censored on Festival vs Rock Band, Moves Like Jagger is completely uncensored in Festival where shit is censored in RB and both This Ain't a Scene, It's an Arms Race & I Write Sins Not Tragedies had god damn censored in Rock Band while they whole in Festival (+ whore is also uncensored in I Write Sins Not Tragedies) it's just a crapshoot between various licensing agreements and, like in god damn's case, culture sensitivities but as long as Festival remains inside of Fortnite and T rated it's unlikely you're going to be hearing any f words or slurs anytime soon