Besides there are two musics playing at the same time, it is impossible to turn off music. Neither turning off the musi nor quiting to main menu does anything; only way to mute the music is to lower the master volume to zero. At first I tried muting the "music volume", and one of the musics stopped (it was one of the old soundtracks of minecraft). However, it started soon after. This happened also in older versions. (probably not that old, only in snapshots of 1.13 update. Still, not so sure...)