Games like Mortifera
Games like Mortifera include Firewatch, Poppy Playtime, MiSide, What Remains of Edith Finch, and Escape the Backrooms. We matched them by the tags players give Mortifera on Steam (Horror, Psychological Horror, Thriller, Mystery, and Singleplayer): closest matches first, and among equally close ones the better-known games.

Firewatch
Shared: Adventure · Mystery · Singleplayer

Poppy Playtime
Shared: Horror · Singleplayer · Psychological Horror

MiSide
Shared: Psychological Horror · Horror · Singleplayer

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

Escape the Backrooms
Shared: Horror · Psychological Horror · Exploration

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

Outer Wilds
Shared: Mystery · Exploration · Adventure

The Park®
Shared: Horror · Psychological Horror · Singleplayer

Psalm 5:9-13
Shared: Horror · Psychological Horror · Mystery

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

Garten of Banban
Shared: Horror · Psychological Horror · Singleplayer

Fears to Fathom - Ironbark Lookout
Shared: Horror · Psychological Horror · Thriller

Five Nights at Freddy's: Security Breach
Shared: Horror · Singleplayer · Exploration

Subliminal
Shared: Psychological Horror · Singleplayer · Horror

Phasmophobia
Shared: Horror · Psychological Horror · First-Person

DREDGE
Shared: Exploration · Adventure · Mystery

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

Firework
Shared: Horror · Psychological Horror · Mystery

Mouthwashing
Shared: Horror · Psychological Horror · Thriller

The Room Two
Shared: Mystery · Horror · Adventure

Outlast
Shared: Horror · Psychological Horror · Singleplayer

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

SOMA
Shared: Horror · Psychological Horror · Exploration

Fears to Fathom - Woodbury Getaway
Shared: Psychological Horror · Horror · Adventure