J.K. Rowling published The Ickabog under her own name rather than a pseudonym.
The Ickabog is a children’s fantasy novel that Rowling wrote during the period when she was developing the Harry Potter books. She described it as a standalone fairy tale, separate from the Harry Potter world. Rowling first released it online in installments in 2020, during the COVID-19 pandemic, before a print edition followed later that year.
The story is set in the fictional kingdom of Cornucopia and centers on a legendary monster called the Ickabog. Rowling invited children to submit artwork for the printed edition, and selected illustrations appeared in the book. Proceeds from the author’s royalties were intended to support groups affected by the pandemic.
This question can be confused with Rowling’s crime fiction, which she published as Robert Galbraith. The Ickabog was not part of the Cormoran Strike series, and it was not marketed as a Harry Potter companion volume.