This point was already clearly made by Awoo's comment but I want to drive it home verbally. Rowling's importance in the anti-trans "movement" has little to do with her popularity as a celebrity which has waned significantly over the years (and was never deserved though it rarely is), but it has everything to do with the fact she is now a billionaire. Because of her vast wealth she gets to dole out funding by the tens and hundreds of millions to the individuals and groups of her choice, handpicking those who will turn that wealth into terror campaigns that have real, quantifiable material effects on the oppression and persecution of trans people. This is because, especially in capitalism, wealth is power and the flow of currency is like the flow of energy in a system. She is a prominent central node in the anti-trans "movement" not because people still think she's a good writer but because the wealth like energy flows from her outward, percolating out to the bigots who actually use it to materially influence policy as well as public sentiment. This billionaire has made it her actual life's work to try to eradicate trans people by ensuring they have no place in society and she has had more than a little degree of success towards that end purely by virtue of the fact that she was able to hoard such an obscene amount of wealth (which is stolen labor at the end of the day). She may have been able to do that initially by being a popular writer, but at this point no one even needs to know her name in order for her to be that central node in a greater system of cruelty and despair (since a system is what it does).