I enjoyed it too, so i understand where you’re coming from. Rowling is a gripping author, and i found myself as a kid flicking a stick and thinking for a fleeting moment that HP magic was real.
Lots of kids did. They got lost in the stories and found themselves in some of the characters. I sure did.
And that’s the main reason why it’s not kosher. I don’t know if HP magic is in the same category as kishuf, ov, yidoni, etc…it doesn’t involve subservience to kochos, avodah zara, or messing with the pamalah shel maalah. I can hear both sides to that
But what is more problematic is that it’s a godless world. Evil is portrayed not as that which Hashem hates, but as racism. The characters possess a mix of morals, with some heros behaving in ways which are disgusting from a Torah perspective.
So a combination of bad morals, a torah-less and God-less world, with a writer who can manipulate the minds of children and have them at the edge kf their seat as they read and imagine…that is harmful for chinuch, and it’s harmful for adults too. The influence is profound.
We live in a world of hester panim, where we have to struggle and claw our way into seeing a glimmer of ruchnius in our lives, we need to constantly fortify our worldview and our priorities..
Divrei Torah are hard to aquire as gold but as easy to lose as glass, chazal say. Our minds are fragile; can we leave them at the mercy of a non jewish author who paints a world devoid of torah and Hashem? Will that not influence us when we have nisyonos?