Limit the headphone volume
You can limit the maximum headphone volume for music and videos to protect your hearing.
Go to Settings > Sounds > Reduce Loud Sounds.
Turn on Reduce Loud Sounds, then drag the slider to choose the maximum decibel level for headphone audio.
Note: If you have Screen Time turned on in Settings, you can prevent changes to the maximum headphone volume. Go to Settings > Screen Time > Content & Privacy Restrictions > Reduce Loud Sounds, then select Don’t Allow.