Anyway, what "worldbuilding" specifically means *as distinct* from all of the above is extratextual, canonical lore, made possible by the idea of a fixed "secondary world" created by the author.

I was going to get picky about this, based on your first post, but speaking as a prof who spends a LOT of time with SFF, I think this is really good, compact understanding of it.

This is what "worldbuilding" as a concept brings to the table as distinct from long-established literary concepts like "setting" or "background." Since this is what makes it unique, this is generally what its critics mean when they (we) have something to say about it.

By "extratextual" and "canonical" are you talking about stuff that's not in the story like a blog post by the author, or something else?