Games like Delirium
Games like Delirium include Layers of Fear (2016), Mouthwashing, Poppy Playtime, Garten of Banban, and Outlast. We matched them by the tags players give Delirium on Steam (Psychological Horror, Horror, 3D, Atmospheric, and Walking Simulator): closest matches first, and among equally close ones the better-known games.

Layers of Fear (2016)
Shared: Psychological Horror · Horror · Atmospheric

Mouthwashing
Shared: Psychological Horror · Horror · Atmospheric

Poppy Playtime
Shared: Horror · Psychological Horror · Singleplayer

Garten of Banban
Shared: Horror · Psychological Horror · Singleplayer

Outlast
Shared: Horror · Psychological Horror · Atmospheric

Summer of '58
Shared: Horror · Psychological Horror · Atmospheric

SOMA
Shared: Psychological Horror · Horror · Atmospheric

MiSide
Shared: Psychological Horror · Horror · 3D

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

No, I'm not a Human
Shared: Psychological Horror · Horror · Atmospheric

Phasmophobia
Shared: Horror · Psychological Horror · Dark

Outlast 2
Shared: Psychological Horror · Horror · Atmospheric

Garten of Banban 2
Shared: Horror · Psychological Horror · Singleplayer

From The Darkness
Shared: Psychological Horror · Horror · Dark

Firewatch
Shared: Atmospheric · Walking Simulator · Mystery

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

Still Wakes the Deep
Shared: Psychological Horror · Horror · Walking Simulator

Visage
Shared: Psychological Horror · Horror · Dark

ROUTINE
Shared: Psychological Horror · Atmospheric · Horror

Welcome to Kowloon
Shared: Horror · Psychological Horror · Atmospheric

Little Nightmares II
Shared: Horror · Psychological Horror · Atmospheric

Psalm 5:9-13
Shared: Psychological Horror · Horror · Walking Simulator

Buckshot Roulette
Shared: Horror · Dark · 3D

DON'T SCREAM
Shared: Psychological Horror · Horror · Atmospheric