Is ONE PIECE episode 880 filler?
Canon No, episode 880 of ONE PIECE is canon.
#880
Sabo Goes into Action! All the Captains of the Revolutionary Army Appear!
サボ動く 革命軍全隊長登場！
Aired 14 Apr 2019
Mochibayo compiled this list from MyAnimeList's labels, because MyAnimeList's episode data is not reaching us at the moment.