Games like Submechanic
Games like Submechanic include Subnautica, Outlast, Subnautica 2, Poppy Playtime, and Firewatch. We matched them by the tags players give Submechanic on Steam (Horror, Underwater, First-Person, Atmospheric, and Linear): closest matches first, and among equally close ones the better-known games.

Subnautica
Shared: Horror · Underwater · First-Person

Outlast
Shared: Horror · First-Person · Atmospheric

Subnautica 2
Shared: Horror · Underwater · First-Person

Poppy Playtime
Shared: Horror · First-Person · Singleplayer

Firewatch
Shared: Atmospheric · Adventure · First-Person

Five Nights at Freddy's: Security Breach
Shared: Horror · First-Person · Singleplayer

MiSide
Shared: Horror · First-Person · Atmospheric

Five Nights at Freddy's: Secret of the Mimic
Shared: Horror · First-Person · Adventure

Subnautica: Below Zero
Shared: Underwater · Horror · Singleplayer

Iron Lung
Shared: Horror · Atmospheric · Underwater

Little Nightmares
Shared: Horror · Atmospheric · Adventure

Little Nightmares II
Shared: Horror · Adventure · Atmospheric

BioShock™ Remastered
Shared: Horror · Atmospheric · First-Person

Layers of Fear (2016)
Shared: Horror · Atmospheric · First-Person

Bendy and the Dark Revival
Shared: Horror · First-Person · Singleplayer

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

Choo-Choo Charles
Shared: Horror · First-Person · Singleplayer

The Forest
Shared: Horror · Adventure · First-Person

Lethal Company
Shared: Horror · First-Person · Atmospheric

Escape the Backrooms
Shared: Horror · First-Person · Adventure

Hello Neighbor 2
Shared: Horror · First-Person · Adventure

Garten of Banban
Shared: Horror · First-Person · Singleplayer

Amnesia: Rebirth
Shared: First-Person · Horror · Adventure

The Beast Inside
Shared: Horror · First-Person · Adventure