@Scraggythang
This book doesn’t sound like it was written by an adult.
Also this line “How can someone who created fantasy novels possibly think biological sex is real”she wonders.
That pretty much sums up the anger towards JK. And when you read it like that, that so many think it is outrageous that she can both be a writer of fiction AND still believe in reality, you do have to laugh.
She has a fundamental misunderstanding of the fantasy genre and how it works.
Fantasy literature only works if the structure around the fantasy elements is stable and works to an understandable set of laws. As a result, a lot of fantasy literature tends to use historical or old-fashioned social and cultural environmental anchors.
A perfect example of this is the narrative of Harry Potter taking place in an environment that is pretty much an English boarding school of the 1930s. Or Lord of the Rings taking place within a Dark Ages environment where a strict patriarchal hierarchy is the backbone of the society. Same goes for A Song of Ice and Fire, and a million other high fantasy novels.
Even in urban fantasy, you get aspects that are out of time: people going to libraries, for example, or an obsession with manuscripts, or buildings that date back hundreds of years, or rather anachronistic policemen that really belong in a Chandler novel.
Fantasy needs these anchors so readers have something to tether their "suspension of disbelief" balloons; otherwise, the narrative is too nebulous and readers either don't understand what the hell is going on or assume the narrative is some kind of fever dream where all meaning is free-floating and thus meaningless.
There are fantasy novels where characters are transgender or non-binary, but what you tend to find is that those characters exist within recognisably formal, conservative and historical structures: for example, pseudo-monastic institutions or as civil servants within an imperial government environment -- you know, generally, what should be expected of them outside their gender expression.
Indeed, there's probably a very interesting piece of work in what fantasy literature reveals about queer theory.
I would argue that fantasy novelists are essentially manipulating "anti-reality" tools to create meaning about reality itself. Of course, you can't do any of that if you don't have a decent grasp on material reality in the first place.