Games like Terrarium II
Games like Terrarium II include Terraria, Webbed, Thank Goodness You're Here!, Slime Rancher, and Momodora: Reverie Under The Moonlight. We matched them by the tags players give Terrarium II on Steam (Choose Your Own Adventure, Exploration, Side Scroller, 2D Platformer, and Collectathon): closest matches first, and among equally close ones the better-known games.

Terraria
Shared: Sandbox · Exploration · Adventure

Webbed
Shared: 2D Platformer · Exploration · Cute

Thank Goodness You're Here!
Shared: Exploration · Adventure · 2D Platformer

Slime Rancher
Shared: Exploration · Adventure · Cute

Momodora: Reverie Under The Moonlight
Shared: Side Scroller · 2D Platformer · Exploration

60 Seconds! Reatomized
Shared: Choose Your Own Adventure · Exploration · 2D

A Short Hike
Shared: Exploration · Adventure · Casual

Hollow Knight
Shared: Platformer · Exploration · 2D

Rain World
Shared: Exploration · Platformer · 2D Platformer

Starbound
Shared: Sandbox · Adventure · Exploration

DAVE THE DIVER
Shared: Exploration · Casual · Adventure

A Hat in Time
Shared: Collectathon · Exploration · Cute

FEZ
Shared: Exploration · Platformer · Casual

60 Seconds!
Shared: Choose Your Own Adventure · Exploration · Point & Click

Afterimage
Shared: 2D Platformer · Side Scroller · Exploration

Mon Bazou
Shared: Exploration · Choose Your Own Adventure · Sandbox

Keplerth
Shared: Exploration · Sandbox · Adventure

鬼谷八荒 Tale of Immortal
Shared: Choose Your Own Adventure · Sandbox · Exploration

Luna's Fishing Garden
Shared: 2D Platformer · Collectathon · Sandbox

Disney Dreamlight Valley
Shared: Exploration · Sandbox · Adventure

Celeste
Shared: 2D Platformer · Platformer · Indie

Hollow Knight: Silksong
Shared: Exploration · Platformer · 2D

Yonder: The Cloud Catcher Chronicles
Shared: Exploration · Adventure · Sandbox

Haiku, the Robot
Shared: Exploration · Adventure · 2D Platformer