Games like Project Proxima
Games like Project Proxima include SOMA, Outer Wilds, Lethal Company, Outlast, and Inside the Backrooms. We matched them by the tags players give Project Proxima on Steam (Adventure, Horror, Atmospheric, Psychological Horror, and Pixel Graphics): closest matches first, and among equally close ones the better-known games.

SOMA
Shared: Horror · Atmospheric · Psychological Horror

Outer Wilds
Shared: Adventure · Space · Exploration

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

Outlast
Shared: Horror · Atmospheric · Psychological Horror

Inside the Backrooms
Shared: Horror · Psychological Horror · Adventure

Iron Lung
Shared: Horror · Atmospheric · Psychological Horror

ROUTINE
Shared: Atmospheric · Psychological Horror · Adventure

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

Alien: Isolation
Shared: Horror · Atmospheric · Sci-fi

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

Escape the Backrooms
Shared: Horror · Psychological Horror · Adventure

Subnautica 2
Shared: Horror · Adventure · Exploration

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

Moons of Madness
Shared: Adventure · Horror · Space

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

Darkwood
Shared: Horror · Adventure · Psychological Horror

No Man's Sky
Shared: Space · Adventure · Exploration

Little Nightmares II
Shared: Adventure · Horror · Atmospheric

Endacopia
Shared: Adventure · Horror · Psychological Horror

Dead Space
Shared: Horror · Space · Psychological Horror

IMSCARED
Shared: Horror · Psychological Horror · Adventure

Backrooms: Escape Together
Shared: Horror · Psychological Horror · Atmospheric

Prey
Shared: Horror · Atmospheric · Space

Firewatch
Shared: Adventure · Atmospheric · First-Person