Games like The Sunday
Games like The Sunday include MiSide, Escape the Backrooms, Ready or Not, Poppy Playtime, and Outlast. We matched them by the tags players give The Sunday on Steam (Horror, Psychological Horror, Adventure, Psychedelic, and 3D): closest matches first, and among equally close ones the better-known games.

MiSide
Shared: Psychological Horror · Horror · First-Person

Escape the Backrooms
Shared: Horror · Psychological Horror · First-Person

Ready or Not
Shared: Realistic · Horror · Psychological Horror

Poppy Playtime
Shared: Horror · Psychological Horror · First-Person

Outlast
Shared: Horror · Psychological Horror · First-Person

Layers of Fear (2016)
Shared: Horror · Psychological Horror · First-Person

Garten of Banban
Shared: Horror · Psychological Horror · First-Person

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

Five Nights at Freddy's: Security Breach
Shared: Horror · First-Person · Singleplayer

Backrooms: Escape Together
Shared: Horror · Psychological Horror · First-Person

The Beast Inside
Shared: Horror · Adventure · First-Person

Visage
Shared: Horror · Psychological Horror · First-Person

Buckshot Roulette
Shared: Horror · First-Person · 3D

Blair Witch
Shared: Horror · Psychological Horror · Adventure

Phasmophobia
Shared: Horror · Psychological Horror · First-Person

Outlast 2
Shared: Horror · Psychological Horror · First-Person

Dark Deception
Shared: Horror · Psychological Horror · First-Person

Subliminal
Shared: Psychological Horror · Horror · Realistic

Little Nightmares II
Shared: Horror · Adventure · Psychological Horror

Lethal Company
Shared: Horror · First-Person · Psychological Horror

Five Nights at Freddy's
Shared: Horror · Psychological Horror · Singleplayer

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

From The Darkness
Shared: Horror · Psychological Horror · First-Person

Inside the Backrooms
Shared: Horror · Psychological Horror · Adventure