Is the iphone 12 dual voltage for european travel?

No need to buy a converter since all Apple products are 100-240 Volt, and 50/60 Hz, but you will need a wall plug adapter for the country to which you are traveling.

You can find these at airports, travel shops and most hotels as well as Amazon.....if you want to buy ahead of time.

As you can see here, you may use 100 to 240 volts to charge your iPhone.

Important safety information for iPhone - Apple Support