I don’t like Harry Potter to begin with, but I don’t really have a huge problem separating the artist from the art if the only thing they did was be hateful.
Roald Dahl was a major antisemite, but I still think he wrote great children’s books and suspense/horror stories. H. P. Lovecraft was bigoted about pretty much anyone who wasn’t a white man. Again, a really good writer.
Where is becomes hard to separate them is when they actually do something about their disgusting ideas. Roman Polanski and Woody Allen are pedophiles. I will never watch either of their movies. And I think both have made very good movies. I feel that I was wrong to watch the ones I did.
So yeah, Rowling is an utterly contemptible piece of shit, but if you like Harry Potter, it’s okay.