Versions 0.217.40 and later of Valheim has moved from using Unity's standard asset management to using a custom asset management system called Soft Referencable Assets that loads assets via Asset Bundles. This enables the game to load and unload assets on the fly, rather than always keeping everything in memory, which saves massive amounts of RAM.
To assist the modding community in this transition, we've collected some common questions and answer them here.