>seperate the fan fiction and maintain consistency during world building

Until even the original author retcons the heck out of their world and goes against established, explicit, well explained lore

Star Wars and the MCU are awful examples to use for the idea that canon can be used for consistency and authoritativeness

History? In the days before books were common stories were not told from written pages but memory. This allowed stories to change and adapt on the storytellers whims (or forgetfulness). Eventually they were ossified in books, of which many people think they are the 'canon'.

I made it up. It's an opinion

The latest commit where the master branch finds itself in isn't any more "true" or genuine than the first commit in history, nor the commits on a fork, nor the commit on branch-1, nor the commit on branch-2

If it's all fiction anyway there is no truth out there for the map to be compared against. All permutations are real, all maps are the territory

I do find it amusing, however, that depending on context people consider the first commit in history to be canon, while on other cases they prefer the newest commit approved by the Authority™