The Wikipedia also says

the term Holocaust is sometimes used to include the murder and persecution of non-Jewish groups, such as the Romani and Soviet POWs.

And I disagree, because it's not sometimes. It's most of the time.

Encyclopedia Brittanica: Holocaust, the systematic state-sponsored killing of six million Jewish men, women, and children and millions of others by Nazi Germany

History.com: The Holocaust was the state-sponsored persecution and mass murder of millions of European Jews, Romani people, the intellectually disabled, political dissidents and homosexuals by the German Nazi

See, I think it's really irresponsible to do as Rowling does and make the Holocaust solely about Jewish people and not the other groups.

First, the etymological argument. Holocaust means whole-burning. Not Jew-burning. It's not called the Loudaicaust, is it? Indeed, according to Wikipedia, people used to say "The Jewish holocaust" up until special importance was assigned to the Jewish persecution and people began to conflate the two.

Second and more importantly, the ethical argument. When we assign special importance to the persecution of Jewish people, we forget the historical oppression of other groups. Which is exactly what Hitler, Rowling, and Netanyahu want us to forget. All three are aligned as fascists who want to tear down history and forget the suffering of those they deem subhuman. Anti-semitism does not exist in a vacuum. It always operates as part of a broader ideology we call fascism. The ideology of all three of these people. The Holocaust is what the fascists did. They did it to many different people. Never forget.

And finally, you moved the goalposts. When you cited Jewish News UK, your position was that she didn't deny the persecution of trans people, because that's what Jewish News said. You've already lost the argument, and now you're trying to save face for Rowling by quibbling over technicalities.

On your last paragraph, I know. Rowling is a Nat-Z as well. That’s why I found it extremely unlikely that she’s a Holocaust denier

What do you mean by this? Aren't most Nazis denying the Holocaust?

and why I used a Jewish supremacist source as they would never let that slide.

I'd argue the opposite. Supremacists of any kind don't care about facts and only care about "their side"