While I am in the group of people that likes to listen to music in the car, and appreciate this feature, the most simple way that I found to stop playback, is to set the iPhone to pause streaming audio in Control Center. The upper-right widget there would have a pause/play button for media playback. You can also ask Siri to “turn off the music”.
Else your car’s media system may have settings to prevent auto-play from connected bluetooth devices.
If you want to dabble in Shortcuts automations, then you can alternative opt for that:
- Open your iPhone's Shortcuts app.
- Search for the Automation tab at the bottom of the toolbar and click on it.
- At the upper right of the screen, tap on the Plus button.
- Click on create Personal automation.
- Click Bluetooth by scrolling down, then tap on it.
- Check for the name of your car on the list of paired Bluetooth devices, **tap on it, **and select done.
- Right at the top right of the screen, tap "Next" and select "search box" at the bottom of the page.
- Find Pause and check out the "play and pause" action under media.
- Tap Play/Pause when you are back to the Actions page.
- Go to the pop-up menu and choose Pause, tap next, and you're done.
(last bit copied from freeyourmusic — I will test this later myself)
