You might want to try applying the tweaks in this guide - https://www.reddit.com/r/valheim/comments/lizxq9/valheim_fps_fix_benchmark_picture_guide_gained_an/ - and see if that helps you out. Without knowing all your individual specs it's hard to suggest what could be the issue but it's probably something on your machine settings. The tweaks in the guide I linked should help tho.

I'm sure you already have everything updated, but double check your graphics card is updated as well.