Hello ThatGuyIsaac,
Thank you for participating in the Apple Support Communities! We understand that the volume music plays at is limited on your iPhone 12 and you're wondering how to adjust this setting. We'd be happy to help.
From what you described, it sounds like "Reduce Loud Sounds" may have been turned on. Here's how you can turn that feature off:
Headphone notifications on your iPhone, iPod touch, or Apple Watch
- Open the Settings app on your iPhone or iPod touch.
- Tap Sounds & Haptics, then tap Headphone Safety.
- Turn Headphone Notifications on or off.*
You can also turn on Reduce Loud Sounds to automatically lower your headphone volume when it exceeds your set decibel level.
*Due to regulations and safety standards, headphone notifications can’t be turned off in certain countries or regions."
Let us know if there's any change after adjusting that feature.
Cheers!