Games like Pestilence
Games like Pestilence include Mouthwashing, SOMA, No, I'm not a Human, Sally Face - Episode One, and Poppy Playtime. We matched them by the tags players give Pestilence on Steam (Psychological Horror, Horror, Investigation, Mystery, and Atmospheric): closest matches first, and among equally close ones the better-known games.

Mouthwashing
Shared: Psychological Horror · Horror · Atmospheric

SOMA
Shared: Psychological Horror · Horror · Atmospheric

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

Sally Face - Episode One
Shared: Psychological Horror · Horror · Story Rich

Poppy Playtime
Shared: Horror · Psychological Horror · Mystery

Phasmophobia
Shared: Horror · Psychological Horror · Investigation

What Remains of Edith Finch
Shared: Atmospheric · Story Rich · Mystery

MiSide
Shared: Psychological Horror · Horror · Story Rich

Firewatch
Shared: Atmospheric · Mystery · Story Rich

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

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

Outer Wilds
Shared: Mystery · Story Rich · Atmospheric

Little Nightmares II
Shared: Horror · Psychological Horror · Atmospheric

Amnesia: A Machine For Pigs
Shared: Horror · Psychological Horror · Atmospheric

Outlast
Shared: Horror · Psychological Horror · Atmospheric

Fran Bow
Shared: Psychological Horror · Horror · Story Rich

Little Nightmares
Shared: Horror · Atmospheric · Psychological Horror

Detention
Shared: Horror · Psychological Horror · Atmospheric

Unheard - Voices of Crime
Shared: Mystery · Thriller · Crime

Firework
Shared: Horror · Psychological Horror · Mystery

Still Wakes the Deep
Shared: Psychological Horror · Horror · Story Rich

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

The Painscreek Killings
Shared: Investigation · Mystery · Horror

Outlast 2
Shared: Psychological Horror · Horror · Atmospheric