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