The reason why the background music in the courtyard of Yin-Yang Teacher has not changed is that it needs to be changed manually. According to the relevant public information displayed in the inquiry, the specific operation steps are as follows:

1. Open the game, paddle the courtyard to the right, and hang a bell on the eaves on the far right.

2. Click this bell, and a list of changing courtyard background music will appear.

3. Different courtyard backgrounds will have different background music. Here, only all the courtyard backgrounds and music of the players are displayed, and there are recently released music at the bottom. Players can choose to replace them by clicking Expand.