Not an ad hominem but a colloquialism of calling out the appearance of argumentum ad ignorantiam.
You appear to be implying the assertion that transphobes like Rowling are NOT claiming that trans people do not have a right to exist and attempting to shift the burden of proof to me. In context of Musk and Rowling, the heap of evidence is significant and your apparent assertion is the extraordinary one requiring extraordinary evidence.
This logical fallacy is also most frequently the territory of bad faith actors.
Now, if there was miscommunication, please do clarify as I do not wish to unfairly characterize your comments.