Optimization is kind of an on-going work through a games development, usually the bulk of it is done at the end just before retail release but some can be included in content releases or hot-fixes... it tends to be an incremental process though up till full release.

However, there is a quick pass of tweaks you can do pretty easily may be helpful to getting your computer to work around the CPU load the game currently can cause in certain situations - https://www.reddit.com/r/valheim/comments/lizxq9/valheim_fps_fix_benchmark_picture_guide_gained_an/

When I did these I went from 4 FPS in my village (it was like playing in stop motion lmao) to 70 - 90 pretty evenly.

Hopefully that helps for now :) & Don't worry! Things will improve as the rest of the game content gets built & released over time :) this is just a temp work-around.

Edit: Dropped a word & had to pick it up & put it where it belonged.