Hello! Well, currently the plugin only plays the music while you are inside the player scene. It does not support background playback. Implement that functionality It would require a relatively high modification of the plugin as many additional situations would have to be considered. I hope I have answered your question! A big greeting.
Viewing post in RPG MAKER MZ Plugin: Music Media Player comments
I recommend you use this plugin, maybe it will help you:
https://undermax.itch.io/radio-system