Modder Thrakal has released a new Valheim mod that includes some basic RPG elements. As the name implies, this mod adds an experience and level up system to the game.
In more detail, the mod allows you to gain experience killing monsters and bosses. In addition, each level gained gives you skill points that can be used for different abilities of your character.
This is the most basic RPG system, and most Valheim players will find it interesting. The mod works on both local and dedicated servers, and you can download it from here.