Games like Under The Island
Games like Under The Island include CrossCode, Terraria, Drova - Forsaken Kin, Hogwarts Legacy, and Fallout 4. We matched them by the tags players give Under The Island on Steam (RPG, Action RPG, Exploration, Female Protagonist, and Puzzle): closest matches first, and among equally close ones the better-known games.

CrossCode
Shared: Action RPG · RPG · Female Protagonist

Terraria
Shared: 2D · Sandbox · Exploration

Drova - Forsaken Kin
Shared: RPG · Action RPG · Exploration

Hogwarts Legacy
Shared: RPG · Singleplayer · Exploration

Fallout 4
Shared: RPG · Exploration · Singleplayer

鬼谷八荒 Tale of Immortal
Shared: RPG · Singleplayer · Sandbox

Rise of the Tomb Raider™
Shared: Female Protagonist · Exploration · Singleplayer

The Elder Scrolls IV: Oblivion Remastered
Shared: RPG · Exploration · Singleplayer

Eastward
Shared: Action RPG · RPG · Pixel Graphics

Black Myth: Wukong
Shared: Action RPG · RPG · Singleplayer

Dragon's Dogma 2
Shared: RPG · Action RPG · Singleplayer

Assassin's Creed® Odyssey
Shared: RPG · Exploration · Singleplayer

Fallout: New Vegas
Shared: RPG · Exploration · Singleplayer

Tomb Raider Game of the Year
Shared: Female Protagonist · Singleplayer · Exploration

Alabaster Dawn
Shared: RPG · Action RPG · Puzzle

The Elder Scrolls Online - Standard Edition
Shared: RPG · Exploration · Singleplayer

Oceans Heart
Shared: Action RPG · Exploration · Puzzle

The Witcher 3: Wild Hunt — Remastered
Shared: RPG · Singleplayer · Adventure

DELTARUNE
Shared: RPG · Pixel Graphics · Singleplayer

ENDER MAGNOLIA: Bloom in the Mist
Shared: Female Protagonist · 2D · Action RPG

Fate Seeker II
Shared: RPG · Action RPG · Exploration

Monster Hunter: World
Shared: RPG · Action RPG · Exploration

Tales of the Black Forest
Shared: RPG · Pixel Graphics · Female Protagonist

OneShot
Shared: Pixel Graphics · Puzzle · Singleplayer