How much money is she getting per sold copy?
It's not easy or simple to say, because most of that money will not come from direct royalties but through the value of the intellectual properties that she owns the rights to. The Harry Potter brand is worth billions of dollars, and although most of that is tied up in the various media licenses owned by Warner Bros a significant proportion is still owned by Rowling.
Then there's the even more intangible value. Rowling is given a lot of license and platform because she is still considered by many to be an important and beloved public figure. By refusing to take any kind of stance against her transphobia, you are essentially buying into and vindicating that perception of her. While she has certainly given a great deal of financial support to transphobes (including literal fascists and Christian fundamentalists) what is likely more significant and yet harder to quantify has been the harm she has done by exploiting her public visibility and reach. By keeping her "legacy" relevant, you are perpetuating her status as a public figure and allowing her to continue to do that.
I'm willing to bet that, despite Rowling herself constantly alleging she is being silenced and persecuted by "trans activists", you do not know the name of any trans person who has actually criticized her. That asymmetry has enormous value.
Also, are we talking about individual consumers purchasing the game, or are we still talking about internet personalities covering it? If the latter, those people aren't buying a single copy of the game, they're doing PR. A single copy of the game is probably worth about 60 dollars. Sponsorships for covering a game on youtube or twitch can be worth thousands of dollars, depending on view count.
If someone were to lose respect for me for buying a video game, i would consider them pretty shallow and not really worth my time.
Okay, let me turn that around.
If you are incapable of the most shallow and insignificant gesture of support or respect when the stakes are essentially whether you get to pay money to play a mediocre video game instead of pirating it a few months down the line when someone cracks the DRM, what are you worth? Why is it in anyone's interest to keep you on side or to pretend to respect your decisions?
Because if you can't do that, what are the chances you're going to do anything that is actually difficult?
Furthermore, I can't do anything about JK Rowling. She's a millionaire, if not a billionaire, and she's so far gone into the black hole of TERFdom that there is no reasoning with her. She's a not-particularly-smart person who ended up in a position of extreme wealth because a good editor fixed most of her bad writing, and has now done what extremely rich people do and convinced herself that she's an authority. You can't reason with that kind of Dunning-Kruger bullshit, even if someone like me would ever be in a position to do so.
If I express an interest in what you do or think, it's because part of me believes (however remotely) that you might be salvageable.
