Games like OYASUMII
Games like OYASUMII include Poppy Playtime, Subnautica 2, The Forest, Darkwood, and Mouthwashing. We matched them by the tags players give OYASUMII on Steam (Horror, Adventure, Exploration, Surreal, and Psychological Horror): closest matches first, and among equally close ones the better-known games.

Poppy Playtime
Shared: Horror · Puzzle · Psychological Horror

Subnautica 2
Shared: Horror · Exploration · Survival

The Forest
Shared: Horror · Adventure · Survival

Darkwood
Shared: Horror · Adventure · Psychological Horror

Mouthwashing
Shared: Horror · Psychological Horror · Retro

Inside the Backrooms
Shared: Horror · Psychological Horror · Adventure

Endacopia
Shared: Adventure · Horror · Psychological Horror

Subnautica
Shared: Horror · Exploration · Survival

Outer Wilds
Shared: Exploration · Adventure · Mystery

Outlast
Shared: Horror · Psychological Horror · Adventure

Firework
Shared: Horror · Psychological Horror · Puzzle

Detention
Shared: Horror · Psychological Horror · Adventure

SOMA
Shared: Horror · Psychological Horror · Exploration

Escape the Backrooms
Shared: Horror · Psychological Horror · Exploration

SILENT HILL 2
Shared: Horror · Psychological Horror · Adventure

Little Nightmares II
Shared: Horror · Adventure · Psychological Horror

Subnautica: Below Zero
Shared: Horror · Survival · Exploration

Lethal Company
Shared: Horror · Exploration · Psychological Horror

Little Nightmares
Shared: Horror · Adventure · Atmospheric

Stray
Shared: Adventure · Exploration · Horror

Resident Evil 7 Biohazard
Shared: Horror · Psychological Horror · Survival Horror

Amnesia: The Dark Descent
Shared: Horror · Psychological Horror · Puzzle

DREDGE
Shared: Exploration · Adventure · Horror

No one lives under the lighthouse Director's cut
Shared: Horror · Adventure · Psychological Horror