> When I plug it into the car, it automatically starts playing the same song on Apple Music My car (maybe most?) helpfully sends a "play" command when my phone

> When I plug it into the car, it automatically starts playing the same song on Apple Music My car (maybe most?) helpfully sends a "play" command when my phone connects via Bluetooth. iOS devices play what was last playing, or pass the event to your music app if you've played something else in the meantime. The fix in my case was a Shorcuts automation that gets triggered when the phone connects to your car. I set the volume to max and tell my favorite podcasts app to "Play". If I just wanted an app to always be considered the "last played" app, I'd do something like add a one second delay and then pause. If I used Spotify, I'd also delete Apple Music.