Originally posted by Lucidess:

Options -> Graphics -> change resolution. Check your v-sync settings as well.
If it's not that, then it's probably not Valheim related.

Most likely it is Valheim related. There are many games out there that work with far higher frame rate and a lot smoother. Instead their solution to poor optimization is not to fix issues but rather to increase minimum requirements. I wouldn't be surprised if they never finished this game. It got really popular early on, they got ton of money and now they might just ♥♥♥♥ off with it. Most of the developers do just that with notable exceptions.