Is ONE PIECE episode 805 filler?
Canon No, episode 805 of ONE PIECE is canon.
#805
A Battle of Limits! Luffy and the Infinite Biscuits!
限界勝負 ルフィと無限ビスケット
Aired 17 Sept 2017
Mochibayo compiled this list from MyAnimeList's labels, because MyAnimeList's episode data is not reaching us at the moment.