So many people in fan settings use "canonical" when what they really mean is "textual": what's on the page or onscreen. Thinking about things in terms of text and subtext is much more interesting to me than what's "canon," which is often just a branding exercise

Here's an example of the distinction: Dumbledore being gay. Rowling says he is, which makes it canonical, but it certainly isn't textual (or, if we're being honest, particularly subtextual.) Its canonical status therefore has somewhat limited utility.

Canon is a tool of franchise management and branding--the people who own the IP telling you the prescribed way to think and interact with their property. That can be genuinely useful, but you have to be clear-sighted around what it is.

Therefore, 'making something canon' just means that a company decided to add it to the prescribed reading of the text. Sometimes that's the same thing as making something textual! But not always. The two ideas intersect but aren't the identical.

Knowing how an author/rights-holder wants you to understand their property can be genuinely useful, but it's only binding if you accept the premise that they're in charge of your understanding of a story. I reject that premise. Text and subtext are real. Canon is fake.