Not Completionist, but I am playing a long game that began after H&H released.

You could call it something akin to completionist: "Naivist"

Ignore anything you might learn from the web and resist the itch to look things up. The only knowledge you are allowed to use to focus your preparations is that which you gain by experiment in the game.

Said preparations must include whatever events the boss of the next biome will unleash against your bases once you defeat the current boss, so if you don't know, prepare to the max for everything.

Which could potentially include making every weapon, but I don't go that far. Irl, and in-game, you can't master every weapon. Even so, there is a lot to do. When you play Valheim this way, it is a saga and it is thoroughly engrossing as you make long-range plans and bring them to completion.