Firstly I am still rather new to iPhones. I have an iPhone 14 pro with the newest release version of iOS and use maps for navigation and Spotify for music over Bluetooth in my wife’s car. The onboard navigation lowers the music before giving a prompt, however with maps the volume of the music is most times louder than the directions.
Oh nice, it’s smart of Spotify to have that. There may be a loudness setting for Apple Music in settings if you’re ever listening to that.