unless they specifically asked, you don’t get to tell a fanfic writer you think they mischaracterized the character by the way. because the second someone writes a fanfic about a character, that character becomes the writer’s own version of the character. canon is only a suggestion, but whether or not an author will follow it / how much of canon an author will take is entirely up to them. you don’t get to stick your nose in their world and tell them “hey this is not to my liking therefore I think you’re doing it wrong” when you can simply leave quietly and move on to something else you may enjoy