If you have a spare box you can host your own dedicated. It pretty straight forward, then you are only paying for energy used.

*Edit I've used gportal, and i am actually using it right now. But I have a spare i7 box i intend to set up. Once i have my own personal server running again I will cancel the hosting. Pretty sure you can host this on a raspberry pi

https://www.pcgamer.com/valheim-multiplayer-dedicated-server/