Here is the full list of all 24 Outlast 2 achievements.
Find Lynn
Finish the game
Finish the game in Hard Mode
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
See the distant mines where Lynn is captive
Escape the crucifixion
Escape from the Scalled
Reach the mine facility
Descend into the mines
Reunited with Lynn
Witness the end
Collect 40 documents
Collect all documents
Complete 30 recordings
Complete all recordings
Use 10 bandages
Spend 10 minutes underwater
Use the microphone for 20 minutes
Perform a twelve-meter blood slide
Crawl for 500 meters