It's still way more canon than Shadows of Mordor, the Lord of the Rings Tabletop game, or Rings of Power. Even if it's just notes, it's been well accepted as part of the canon by many people. It's not universally accepted canon, but it's far from 'hard to consider'.
Just like there is plenty of non-Lucas Star Wars material that people would consider canon, even if not completely official or having been rendered non-canon. Stuff like Han shot first is non-canon that is still recognized as canon. Even Solo: A Star Wars Story intends to follow Han Shot First as canon, by the director's own admission.
I personally don't see canon as definitive. I'm more particular to the Wikipedia explanation of the term.
In fiction, canon is the material accepted as officially part of the story in an individual universe of that story by its fan base
It's not just the official version by way of the author, but by what is accepted as official by the fanbase. I think that's a very nuanced, yet important distinction to make. And of course, one that builds infinite arguments amongst the fanbase on what is and isn't 'official'. The term is flexible enough to recognize that Han Shot First can be considered official canon, from a certain point of view.