Games like Mirthwood
Games like Mirthwood include Stardew Valley, Kenshi, Terraria, Rust, and My Time at Portia. We matched them by the tags players give Mirthwood on Steam (RPG, Farming Sim, Sandbox, Open World Survival Craft, and Medieval): closest matches first, and among equally close ones the better-known games.

Stardew Valley
Shared: Farming Sim · RPG · Sandbox

Kenshi
Shared: Sandbox · RPG · Immersive Sim

Terraria
Shared: Sandbox · Open World Survival Craft · Crafting

Rust
Shared: Open World Survival Craft · Crafting · Sandbox

My Time at Portia
Shared: RPG · Farming Sim · Crafting

Valheim
Shared: Open World Survival Craft · Crafting · Survival

Travellers Rest
Shared: Farming Sim · RPG · Medieval

Medieval Dynasty
Shared: Medieval · Crafting · Sandbox

Don't Starve Together
Shared: Open World Survival Craft · Sandbox · Survival

Conan Exiles Enhanced
Shared: Open World Survival Craft · RPG · Sandbox

Project Zomboid
Shared: Open World Survival Craft · Sandbox · Survival

Black Desert
Shared: Sandbox · Medieval · Exploration

The Forest
Shared: Open World Survival Craft · Crafting · Survival

Dinkum
Shared: Open World Survival Craft · Farming Sim · Sandbox

Dune: Awakening
Shared: Open World Survival Craft · Sandbox · Exploration

Life is Feudal: Your Own
Shared: Open World Survival Craft · Medieval · Sandbox

Forager
Shared: Open World Survival Craft · Farming Sim · Sandbox

Kynseed
Shared: Farming Sim · Sandbox · RPG

Crusader Kings III
Shared: RPG · Medieval · Sandbox

The Long Dark
Shared: Open World Survival Craft · Exploration · Survival

Graveyard Keeper
Shared: RPG · Sandbox · Crafting

Starbound
Shared: Sandbox · Open World Survival Craft · Crafting

Potion Craft: Alchemist Simulator
Shared: Crafting · Medieval · Sandbox

Coral Island
Shared: Farming Sim · RPG · Life Sim