The only reason to create a new character or world is to ensure greater content of the new Frost Caves content. The addition of Frost Caves to the mountain biomes of Valheim will only be added to unexplored regions of mountain biomes, previous explored mountain regions will not have any Frost Caves added to them. If when taking a break from the game, back in April 2021, you had not explored that much of your Valheim seed map, there really is no essential reason to create a new world. There is no essential reason to create a new character.