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