Games like Portal Knights
Games like Portal Knights include Terraria, Rust, ARK: Survival Evolved, Valheim, and Raft. We matched them by the tags players give Portal Knights on Steam (Adventure, Multiplayer, Sandbox, RPG, and Building): closest matches first, and among equally close ones the better-known games.

Terraria
Shared: Sandbox · Multiplayer · Adventure

Rust
Shared: Multiplayer · Crafting · Survival

ARK: Survival Evolved
Shared: Multiplayer · Survival · Adventure

Valheim
Shared: Multiplayer · Survival · Building

Raft
Shared: Multiplayer · Survival · Crafting

Enshrouded
Shared: Multiplayer · Survival · Adventure

Once Human
Shared: Multiplayer · Survival · Building

Scrap Mechanic
Shared: Sandbox · Multiplayer · Building

Conan Exiles Enhanced
Shared: Survival · Building · Multiplayer

ARK: Survival Ascended
Shared: Multiplayer · Survival · Adventure

Don't Starve Together
Shared: Multiplayer · Adventure · Survival

Core Keeper
Shared: Multiplayer · Sandbox · Survival

Sons Of The Forest
Shared: Multiplayer · Survival · Co-op

Monster Hunter: World
Shared: Multiplayer · RPG · Adventure

The Forest
Shared: Adventure · Survival · Crafting

Grounded
Shared: Multiplayer · Survival · Adventure

Medieval Dynasty
Shared: Multiplayer · Building · Crafting

Palworld
Shared: Multiplayer · Survival · Adventure

Dune: Awakening
Shared: Adventure · Survival · Sandbox

Project Zomboid
Shared: Multiplayer · Survival · Sandbox

ASTRONEER
Shared: Multiplayer · Survival · Adventure

Satisfactory
Shared: Multiplayer · Crafting · Building

TerraTech
Shared: Sandbox · Building · Multiplayer

Starbound
Shared: Sandbox · Adventure · Survival