Valheim has an active modding community that while not directly supported by a built in mod-loader, free mods and the general modding community are encouraged by the Developers, Iron Gate. As an alternative to official support, the Unity Modding Engine, BepInEx, was configured to work for Valheim and has been successful in becoming the standard method for modding Valheim.
Community made Valheim mods built for BepInEx are hosted on ThunderStore and Nexus. Mods hosted on ThunderStore can be installed on your client manually or using either the ThunderStore Mod Manager or r2modman Mod Manager. Mods hosted on Nexus can also be installed manually or can be installed using the Vortex mod manager.
When modifying your Valheim server, there are two options. You can install Valheim Plus which provides it's own extensive set of configurations as well as a version of BepInEx that's confirmed to work with that version of Valheim Plus, but not necessarily with the latest version of Valheim. Or you can install BepInEx directly, providing support for BepInEx plugins and the latest Version of Valheim, including Valheim Plus, and an otherwise vanilla Valheim experience.
Installing BepInEx Plugins
The process for installing BepInEx plugins on your server is the same for both Valheim Plus and BepInEx because Valheim Plus uses BepInEx already. You just need to download the
.dll file from your preferred mod hosting site, either Nexus or ThunderStore, and upload them to the
/BepInEx/plugins folder on your server using either the File Manager or SFTP.
Some BepInEx plugins will be downloaded a
.zip file that contains a sub folder containing multiple files, often assets for the plugin. You'll need to upload the folder and it's contents to the
/BepInEx/plugins folder. For example, if the decompressed plugin folder contains a subfolder by the name of
plugin you'll want the path of your server to look like