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 B-flat Major Wq. 61-03 (H. 289) is one of his later works, characterized by its free form and improvisational elements. This piece showcases Bachʼs mastery of emotional expression, featuring bold modulations and rhythmic changes that surprise the listener. Particularly striking are the flowing melodies developed from the outset and the contrasting intense passages. In this work, Bach pursues a unique musical language that transcends the boundaries of the Classical era, leaving a profound impression on the audience. Performers are required to have advanced technical skills and expressiveness, allowing for new interpretations with each performance.