To be clear, that’s not a quote from Lithgow. It’s a quote from the author of the article. This is what Lithgow said:

Shortly after he picked up the role, Lithgow received a letter from the mother of a trans-identifying child, titled “An Open Letter to John Lithgow: Please Walk Away from Harry Potter.”

“That was the canary in the coal mine,” Lithgow said. “I thought, ‘Why is this a factor at all?’ I wonder how J.K. Rowling has absorbed it. I suppose at a certain point I’ll meet her, and I’m curious to talk to her.”

When asked if the backlash made him consider ditching the role, though, Lithgow said, “Oh, heavens no.”