This site introduces unknown Emanuel Bach (C. P. E. Bach).
ChatGPT4o writes as follows (please note that it may not be accurate):
Emanuel Bachʼs Fantasia in F-sharp minor Wq. 67 (H. 300) is one of the works that demonstrates his distinctive style. This piece is characterized by improvisational elements and bold harmonic progressions, featuring emotional changes that surprise the listener. It is written in a free form, granting the performer significant expressive freedom. Particularly, the sudden tempo changes and unexpected modulations leave a strong impression on the audience. The richness of Bachʼs emotional expression stands out, making it a pioneering work that transcends the boundaries of classical music. This fantasia offers an excellent opportunity to explore the deep inner world of his music.