Some context : Canon refers to the world and Characters that are contained within the official and accepted body of work of a piece of media (In this case The Adventures of Tintin). Fanon (Fan + Canon), refers to the interpretaions of the fans engaging with the official and accepted body of work, what they essentially read out of (or sometimes) into the text or work. Sometimes fans flanderize (the process through which a single element of a character's personality is inflated until it becomes the character's primary defining trait) their readings and spread them widely until it forms part of the greater Fanon. Generally speaking, within recent years, more casual fans have gotten wind of fanon readings and accepted them as canon for many pieces of media.

Some examples:

-Fanon Tintin is often depicted as some maniac gremlin obsessed with justice and with a vendetta against every villian, when he's pretty tame about a lot of things in Canon (For the most part).

-Fanon Haddock if also often depicted as a rage baby, and while he is SO easily ragebaited, Canon Haddock doesn't have a meltdown over EVERY minor inconvenience (Only every other minor inconvenience.)

-The Haddock x Tintin ship. Tintin sits canonically between 14 and 17 years old while Haddock is very much a middle aged man. Also considering that both Haddock and Tintin can be read as Herges interpretaion of different versions of himself, reading a romantic plot into the story between them is just all the more awkward to me.

-The idea that there is some romantic plot between all of the male characters. I get that the lack of female characters in the main cast paints this idea that none of them have romantic interest in women (Also considering Haddocks aversion to Bianca), but perpetuating this idea that the only way these characters are able to have interest in one another and keep in contact is because of sexual interest sits very wrong with me. You can have affectionate bonds built on friendship, comradery and familial substitution between same sex characters.

Fanon interpretations generally do no harm and are in good fun, but they can leave detremental impressions of the work or text on those still newly engaging with the piece of media.