Here is the full list of all 24 Outlast 2 achievements.
Finish the game
Finish the game in Hard Mode
Witness the end
Reunited with Lynn
Collect 40 documents
Descend into the mines
Use 10 bandages
Reach the mine facility
Complete 30 recordings
Escape from the Scalled
Escape the crucifixion
See the distant mines where Lynn is captive
Find Lynn
Finish the game in Nightmare Mode
Finish the game in Insane Mode
Finish the game without hiding in a barrel or closet
Finish the game in Insane Mode without reloading the camera battery
Finish the game in under 4 hours
Collect all documents
Complete all recordings
Spend 10 minutes underwater
Use the microphone for 20 minutes
Perform a twelve-meter blood slide
Crawl for 500 meters