Games like Investigator
Games like Investigator include Firewatch, Poppy Playtime, Layers of Fear (2016), Blair Witch, and The Long Dark. We matched them by the tags players give Investigator on Steam (Adventure, Indie, Horror, Atmospheric, and Walking Simulator): closest matches first, and among equally close ones the better-known games.

Firewatch
Shared: Adventure · Atmospheric · Walking Simulator

Poppy Playtime
Shared: Horror · Free to Play · Singleplayer

Layers of Fear (2016)
Shared: Horror · Atmospheric · Walking Simulator

Blair Witch
Shared: Adventure · Horror · Indie

The Long Dark
Shared: Atmospheric · Adventure · Singleplayer

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

Little Nightmares
Shared: Adventure · Horror · Atmospheric

Outlast
Shared: Horror · Atmospheric · Adventure

Among the Sleep - Enhanced Edition
Shared: Indie · Horror · Adventure

VERGE:Lost chapter
Shared: Indie · Horror · Adventure

Metro Exodus
Shared: Post-apocalyptic · Atmospheric · Horror

The Hat Man: Shadow Ward
Shared: Indie · Horror · Adventure

Killer Frequency
Shared: Adventure · Horror · Simulation

The Beast Inside
Shared: Adventure · Horror · Indie

Visage
Shared: Horror · Adventure · Atmospheric

[Chillas Art] The Convenience Store
Shared: Indie · Horror · Adventure

Scanner Sombre
Shared: Horror · Adventure · Walking Simulator

METRO 2033 Redux
Shared: Atmospheric · Horror · Post-apocalyptic

The Beginner's Guide
Shared: Indie · Walking Simulator · Atmospheric

Little Nightmares II
Shared: Adventure · Horror · Atmospheric

The Forest
Shared: Horror · Adventure · First-Person

METRO Last Light Redux
Shared: Atmospheric · Post-apocalyptic · Horror

Ultimate Custom Night
Shared: Horror · Free to Play · Singleplayer

Hellblade: Senua's Sacrifice
Shared: Atmospheric · Adventure · Horror