Terf stands for “Trans exclusionary Radical feminist”, which is a type of feminist that pushes for women’s rights, but doesn’t support transgender rights, and thinks MtF transgender people don’t count as women.
A lot of people have boycotted Hogwarts legacy because of her political views. Personally, I think it’s a bit extreme to boycott a great game made by a studio and developers that have nothing to do with her views just because she gets royalties on it, but that’s a matter of personal opinion