Games like Syndrome
Games like Syndrome include Alien: Isolation, Outlast, METRO 2033 Redux, Dead Space, and The Outlast Trials. We matched them by the tags players give Syndrome on Steam (Survival Horror, Horror, Stealth, Psychological Horror, and First-Person): closest matches first, and among equally close ones the better-known games.

Alien: Isolation
Shared: Survival Horror · Horror · Stealth

Outlast
Shared: Horror · Survival Horror · First-Person

METRO 2033 Redux
Shared: Horror · Atmospheric · FPS

Dead Space
Shared: Survival Horror · Horror · Psychological Horror

The Outlast Trials
Shared: Horror · Survival Horror · Psychological Horror

METRO Last Light Redux
Shared: Horror · Atmospheric · FPS

Resident Evil 7 Biohazard
Shared: Survival Horror · Horror · First-Person

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

Dead by Daylight
Shared: Horror · Survival Horror · Stealth

Outlast 2
Shared: Horror · Survival Horror · Psychological Horror

Resident Evil Village
Shared: Survival Horror · Horror · First-Person

SOMA
Shared: Horror · Psychological Horror · Survival Horror

Prey
Shared: Horror · Sci-fi · Space

Metro Exodus
Shared: Horror · FPS · Atmospheric

Dying Light
Shared: Survival Horror · Horror · First-Person

Amnesia: The Bunker
Shared: Survival Horror · Horror · Stealth

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

Dead Space (2008)
Shared: Horror · Survival Horror · Sci-fi

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

Dead Space™ 2
Shared: Survival Horror · Horror · Shooter

CASE: Animatronics
Shared: Horror · Survival Horror · First-Person

Species: Unknown
Shared: Horror · Survival Horror · First-Person

Five Nights at Freddy's
Shared: Horror · Survival Horror · Psychological Horror

The Forest
Shared: Horror · Survival Horror · First-Person