Originally posted by Reece:

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

Or you can just use the in-game graphics settings to do 85% of that. The rest can be done in your GPU control panel or don't matter unless you don't meet system requirements in the first place.