While you can get this trophy for just following butterflies to some treasure - you’ll get them to appear on the map whenever you go close to one - if you wait until after you’ve unlocked your Talents skill tree (or thereabouts), a side quest will pop up in Hogsmeade called “Follow the Butterflies.” Speak to Clementine and then follow the quest to its conclusion. This trophy will pop as soon as you find the treasure. Nice and simple.

After you've finished this side quest, there are still 14 to collect in the open-world, especially if you want the Collector's Edition  trophy. We have a guide for all Hogwarts Legacy butterflies locations you can use for that.