Here is the full list of all 21 Black Mirror achievements. It takes around 6-8 hours to unlock all of the achievements on Windows.
You have met a mysterious boy
You have opened the library cabinet without leaving marks
You have settled in your new home
Margaret and Rosemary have found each other again
You successfully used the dumbwaiter
You have observed Eddie's toy chest
You have entered the hidden caves below the Castle
You have calmed yourself down after a stressful night
You have calmed yourself down three times
An invisible chasm traversed
You have entered the Vision in the Chapel
You have entered the Vision in the Glasshouse
You have lived through the Vision in the Cellar
You have entered the Vision in the Village
You have experienced the Vision in the Master Study
Chapter I completed
Chapter II completed
Chapter III completed
Chapter IV completed
Chapter V completed
You have enjoyed a wonderful Scottish breakfast