One piece and attack on titan both have a fixed end point to the main story. Naruto had its ending. Boruto exists but it is a spinoff. Dragon ball, detective conan.. Etc are the only one's that keep on going. With things like dragon ball being seasonal and detective conan taking more episodic nature. Dragon ball even had its ending by the author. Super only exists because toriyama decided to get back into it and money talks. The concept itself of gods of destruction was great. Movie did well after gt being blah! Which was not canon.
But, largely manga's have starting, middle and end. Characters die or achieve goal. It is nothing like american comics which follow more of an episodic existence and status quo . Mangaka's do take hiatus's. When they do the stories goes to pause like berserk or hunter x hunter. Overall, the manga has the formula of one author, one story and one vision ( except for editorial inputs/medaling. They are a thing even there) unlike American comics. So, i don't agree with manga's have no fixed ending bit. They do. Atleast, most of them do. They have no qualms in ending a franchise and starting a new franchise with a story. Manga's are story focased.in Comics, stories are made for an eternal character. Manga's are not like that. Franchises like fullmetal alchemist, bleach.. Etc are all finished stories.
Any material that author or creator hasn't put his approval is considered non canon. Everthing written by the original author is the only one's considered canon.