What Does It Mean That I, the Author, Became the Protagonist of the Novel?

Shi Yan accidentally joined a special group of novel lovers. He received an invitation from the group leader for a novel writing competition, asking him to write a novel without a protagonist. As he gradually completed the setting and worldview construction, he unexpectedly discovered that the plot in the novel reappeared in reality. He began to doubt himself and the world... Once the story starts, it doesn't stop. How does he create a perfect novel? The reference text is as follows: Shared Psychotic Disorders There is a world constructed by multiple mental patients, and other mental patients can be convinced to recognize and join in. Everything they create in their fantasies is recognized by other patients. So is there such a world?