https://wccftech.com/how-to/monster-hunter-rise-sunbreak-how-to-prepare-for-the-expansion-and-access-it/

Monster Hunter Rise: Sunbreak adds new features, monsters, and biomes to the game, new challenging quests, a new home base called Elgado, and much more. However, players that want to join the adventure need to complete the Hunter Rank 7 Hub Quest “Serpent Goddess of Thunder” in the base game before being able to start the new expansion’s quests.

Moreover, equipment and gears might need to be upgraded before dealing with new monsters, as they are more challenging than the ones in the base game. In this guide, you will find all the information you need to prepare for Sunbreak and access the DLC.