When I play Pokemon Ultra Moon on it, the screen is just grey

In order for us to provide better support, we need to see the log generated by Citra. This guide will walk you through how you can obtain the log file: How to Upload the Log File.

the music plays but the screen is just grey

Is this something that started in recent builds? If not, sounds like you might need to update your GPU drivers.

Turn off Enable Hardware Shader in Emulation - Configure - Graphics.

when i turn off hardware shader, there is no save setting button or something like that

The window is too big to see the OK or Cancel options. Try shrinking it down.

since the window is off the screen, my mouse cant go outside of the screen so i dont know how to resize it :confused:

Try double clicking on the top bar that says “Citra Configuration”?