Out of the 15 One Piece movies, none of them are considered canon. However, some of the movies are closely related to the manga/anime and have storylines that directly came from the manga, such as One Piece the Movie: Episode of Arabasta: The Desert Princess and the Pirates and One Piece: Episode of Chopper Plus: Bloom in Winter, Miracle Sakura. One Piece Film: Strong World has creator Eiichiro Oda as the executive producer and he also wrote the story for this. Oda also serves as a general producer for One Piece Film: Z, One Piece Film: Gold, One Piece: Stampede, and One Piece Film: Red.

There are only four One Piece movies out of the 15 total that are considered canon, which are One Piece: Strong World, One Piece Film Z, One Piece Film: Gold, and One Piece: Stampede. One Piece Film: Red could potentially fit into the story after the "Wano Country Arc," but it has not been confirmed to be canon.

Technically speaking, none of the One Piece movies are essential to the original plot of the manga and anime. However, the One Piece movies have standalone storylines that could complement the main story arc. If you are also looking for extra adventures from the beloved Straw Hat crew, then it’s worth watching the movies.