My game was quite laggy when I first got this game, other than reducing effects in the graphics menu this Nexus mod made a Massive difference, basically disables shadow and reflection effects and frees up your processor, its very useful if you have a Potato for a computer.

There are many 'Must Have' mods that really should be apart of the main game settings.

There is a Nexus Mod
ValheimFPSBoost for Valheim

Features:
- Disable Anisotrophic Filtering
- Decrease LOD distance
- Reduce texture size by half
- Set max. pre-rendered frames to 1
- Set particle raycast per frame to 1
- Reduce maximum number of light pixels on an object
- Disables real-time reflection probes
- Disables cascaded shadows
- Disable shadows
- Disables soft blending for particles
- Disables two-pass shader for terrain vegetation
- Disable all Post Processing effects