From the linked article in Entertainment,
However, Rowling has frequently identified with the TERF (trans-exclusionary radical feminist) movement. She has habitually shared anti-trans rhetoric on social media, at one point tweeting that she'd "happily do two years" in prison instead of supporting policies protecting transgender people from hate crimes.
The evidence for this is a hyper link to an article from Entertainment Weekly (the same publication)
When a commenter seemed to reference a report on the U.K.'s Labour Party working to incorporate transphobic abuse — including referring to someone with a pronoun they do not use — under hate crime legislation that would make offenses punishable by up to two years of imprisonment, Rowling essentially said she'd serve her time.
But in reality, what she said was
"I'll happily do two years if the alternative is compelled speech and forced denial of the reality and importance of sex," she wrote on X, formerly known as Twitter.
It is very clear from her words that the issue is not with trans people but with compelled speech, the denial of reality and the importance of actual biological sex