What you want to ask is, is The Mirror Kingdom an Ocean Book mission? Yes. According to the query on the official Genshin Impact website.
1. In version 4.0 of the Genshin Impact game, if you want to complete the world mission in the Ocean Book Fountain map, you need to successfully complete the second and third acts of Narcissus' Ann, The Kingdom in the Mirror. and If she wasn't dreaming, your mission deciphered.
2. "Genshin Impact" is an open-world adventure game produced and distributed by Shanghai MiHoYo Network Technology Co., Ltd. The project was created in late January 2017 and initial testing began in June. September 21, 2019. Open, return testing will begin on March 19, 2020, departure testing will begin on June 11, 2020, technical open testing of the PC version will begin on September 15, and open beta will begin on September 28. 2020. In terms of data, under the same official server, account data between iOS, PC and Android platforms areinteroperable and players can switch devices under the same account.
“If She Stops Dreaming About You” is a scene from one of the chapter missions in the game Genshin Impact, so there aren't many chapters that are just just one scene.
According to the query on Jiuyou.com, in the game Genshin Impact, there are two mission chapters in the Ocean Book in the Fountain area, namely "Ancient Color" and "Anna of Narcissus". These two tasks each have three small tasks: the old color task is divided into three acts, namely: "Sea foam and flowing red paint", "Dream and ocher gradient", "Heart and blue moon" "Missing"; Narcissus' mission is also divided into three acts, namely: "The Adventure of Narcissus' Cross", "The Kingdom in the Mirror" and "If She Stops Dreaming of You...". So, "If she stops dreaming about you" is a scene from one of the missions in the chapters of the game Genshin Impact, so there aren't many chapters that are just one scene.