Here is the full list of all 12 The Backroom - there are Lost and Found achievements.
Find all the Almond Waters during a single playthrough.
Find the lost one
Find another lost one
Find the last one
Find your way out of the Backrooms
Find all the paintings
Complete the game under 20 minutes
...in the backrooms
Goes on and on!
During "The Found", find all zebras.
Complete the game in the "The Found" -mode.