Players who own the game on the original Switch will only need to pay a small additional fee to upgrade to the Switch 2 edition.
This means you can enjoy the latest version without purchasing the game again in full. The upgrade process is designed to be simple and affordable, making the transition smooth for existing users.
https://www.shacknews.com/article/146594/animal-crossing-new-horizons-switch-2-5-dollar-upgrade