Cool game, it was somehow pretty fun having to keep track of all the letters. Okay so you wanted me to list off some stuff that I think can be improved:
The music was just a bit too repetitive and kinda annoying to listen to. It was a bit unclear at first that you had to press the buttons, not the notes because the buttons didn't really look like buttons. And you should probably not include the tutorial inside the scene you are playing in, didn't have time to read them, had to read them on the itch page. Can't really think of much else that needs to be improved honestly. Great job with the game!