Games like The Imagined Leviathan: Prologue
Games like The Imagined Leviathan: Prologue include SOMA, Still Wakes the Deep, Firewatch, What Remains of Edith Finch, and Layers of Fear (2016). We matched them by the tags players give The Imagined Leviathan: Prologue on Steam (Psychological Horror, Horror, Lovecraftian, Atmospheric, and Walking Simulator): closest matches first, and among equally close ones the better-known games.

SOMA
Shared: Psychological Horror · Horror · Atmospheric

Still Wakes the Deep
Shared: Psychological Horror · Horror · Lovecraftian

Firewatch
Shared: Atmospheric · Walking Simulator · Mystery

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

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

Outlast
Shared: Horror · Psychological Horror · Atmospheric

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

DREDGE
Shared: Lovecraftian · Exploration · Psychological Horror

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

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

Dagon: by H. P. Lovecraft
Shared: Horror · Lovecraftian · Atmospheric

The Long Dark
Shared: Atmospheric · Exploration · Survival

Call of Cthulhu®
Shared: Horror · Psychological Horror · Lovecraftian

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

Outer Wilds
Shared: Exploration · Mystery · Atmospheric

Mouthwashing
Shared: Psychological Horror · Horror · Atmospheric

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

ROUTINE
Shared: Psychological Horror · Atmospheric · Horror

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

Metro Exodus
Shared: Post-apocalyptic · Atmospheric · Horror

Subnautica 2
Shared: Horror · Exploration · Survival

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

Fallout 4
Shared: Post-apocalyptic · Atmospheric · Exploration

Outlast 2
Shared: Psychological Horror · Horror · Atmospheric