You may be disappointed by what I said, but it is a reality. The enrollment of music majors in the Conservatory of Music is very small, and some even recruit only a few. Especially for the majors of composition and command, the requirements are quite high. I can see from your introduction that your musical ability is very poor. "I have never learned solfeggio at all, but I know a little about music theory." Is not enough. Really, I didn't mean to throw cold water on you. At present, all the candidates who take the music major in the Conservatory of Music have a high level, and many of them have even won professional competitions.

However, in my opinion, you must first enter the non-music major of the Conservatory of Music, such as music management major, and then try to change your major, or take the course of composition conductor to realize your desire to learn composition. Of course, it must be feasible. If it is not feasible, it is no use.