I want to answer this vaguely because I honestly don't care about Rowling at all, nor what out of touch famous people think about anything regarding real life.
It doesn't really matter what people say or do anymore, all that matters is what we are told to think about them mixed with general cancel culture. To take someone totally different, look what happened to Depp, or look at Manson being canceled once again for the same nonsense reasons and still with no evidence. They were guilty until proven innocent because we were told so, and there's sadly nothing more to it.
Is Rowling transphobic? In the end it no longer matters, that's what the people of high symbol/object value say, therefore it is true.