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 D minor (Wq. 117/12) is characterized by its empfindsamer Stil, an improvisational and emotionally rich expression. This piece, written in the mournful key of D minor, is notable for its deep lyricism and dramatic elements. The free form and unpredictable harmonic progressions evoke strong emotional responses from both performers and audiences. The use of ornamentation and rhythmic variations further enhances the expressiveness of the piece, creating a dense musical world despite its brevity. Performers are required to possess a high level of sensitivity to convey the improvisational nature of this work.