Games like 6 rooms
Games like 6 rooms include Firewatch, What Remains of Edith Finch, Outer Wilds, The Exit 8, and Poppy Playtime. We matched them by the tags players give 6 rooms on Steam (Adventure, Realistic, Horror, Puzzle, and Atmospheric): closest matches first, and among equally close ones the better-known games.

Firewatch
Shared: Adventure · Atmospheric · Walking Simulator

What Remains of Edith Finch
Shared: Atmospheric · Adventure · Walking Simulator

Outer Wilds
Shared: Adventure · Exploration · Atmospheric

The Exit 8
Shared: Puzzle · Horror · Exploration

Poppy Playtime
Shared: Horror · Puzzle · Adventure

Layers of Fear (2016)
Shared: Horror · Atmospheric · Walking Simulator

Inside the Backrooms
Shared: Horror · Puzzle · Adventure

INFRA
Shared: Puzzle · Adventure · Atmospheric

Stray
Shared: Adventure · Atmospheric · Exploration

Amenti
Shared: Adventure · Horror · Atmospheric

Riven
Shared: Adventure · Puzzle · Exploration

Killer Frequency
Shared: Adventure · Horror · Puzzle

Little Nightmares II
Shared: Adventure · Horror · Puzzle

Little Nightmares
Shared: Adventure · Horror · Atmospheric

Amnesia: A Machine For Pigs
Shared: Horror · Walking Simulator · Atmospheric

SOMA
Shared: Horror · Atmospheric · Exploration

The Painscreek Killings
Shared: Puzzle · Horror · Exploration

Quern - Undying Thoughts
Shared: Adventure · Puzzle · Atmospheric

Scanner Sombre
Shared: Horror · Adventure · Walking Simulator

Backrooms: Escape Together
Shared: Horror · Realistic · Atmospheric

The Death | Thần Trùng
Shared: Horror · Adventure · Puzzle

The Vanishing of Ethan Carter
Shared: Atmospheric · Adventure · Walking Simulator

The Room Two
Shared: Puzzle · Adventure · Atmospheric

Fears to Fathom - Ironbark Lookout
Shared: Horror · Atmospheric · Adventure