Please understand that from a business perspective the only thing that spending money on official Harry Potter things does is send the message that JK Rowling is the exact opposite of a liability: It tells companies she brings profits.
I see multiple people around social media saying that they are going to assuage their guilt about anything they buy related to Harry Potter by donating an equal or greater amount to some form of transgender related charity.
While I am sure the charities in question appreciate the cash no matter what inspired the donation, I can assure you exactly no one at, say, Warner Brothers gives a flying fuck.
You could spend five cents on Harry Potter gum and a million dollars on The Trevor Project and the only thing which matters to JKR's career is the four cents profit on gum.
If JKR turns a profit then she gets ANOTHER book deal, ANOTHER movie, ANOTHER officially branded tie-in item which sadly bears too much resemblance to a vibrator, or whatever. Your specific money helps that. Period.
This is not equal and opposite. Exactly no company on this planet has an intern tracking whether donations to transgender related charities go up at the same rate as sales on that upcoming Harry Potter game. They track one figure and one figure only: Did we make money?
I know it's hard. I know we loved the books, and the stories, and got a tattoo or visit the theme park every year or have an entire wardrobe in the colors of your Hogwarts house or what have you. I KNOW. Ravenclaw pride right here, what what! BUT IT DOES NOT MATTER.
If your goal is to take a financial stand against JKR then the equal or higher donation method does not do that. Your money encourages her career. Period.
Now I am not your therapist or religious advisor or god or talking cricket. It's not for me to tell anybody how they should protest. (If you want my personal stance: I am all aboard team JKR has relinquished rights. The concept is ours now. Go forth and give money to fan artists and crafters instead. But again, that's me. Your mileage may vary.)
All I am saying is that if someone says their chosen method is not to support JKR financially that means their money has to stop flowing in Jo's direction.
It's no different than if somebody said they wanted to buy pizza so they're going to head to McDonald's: I'm not telling you whether or not you should have pizza, I'm telling you the golden arches does not sell it.
In conclusion, trans rights are human rights and JK Rowling can go fuck herself because god knows I'd never touch her.