Here is the full list of all 31 A Castle Full of Cats achievements. It takes around 1-2 hours to unlock all of the achievements on Windows.
Find all cats in the library
Find all the cats
Find the crystal ball upgrade
Find all cats in the bedroom
Find all cats in the pantry
Find all cats in the main hall
Release Fofiño from the curse
Meet everyone at the final door
Find all cats in the trapdoor
Find all cats in the secret trapdoor
Return all the kittens to mama cat
Find the hidden castle map
Find all cats in the cell III
Find all cats in the castle
Help a friend from the underground
Deliver the snack
Find all cats in the saferoom
Open the passage
Find all the keys
Find all cats in the cemetery
Unlock a magical shortcut
Find all cats in the mirror passage
Find all cats in the underground corridor
Find all cats in the kitchen
Find all cats in the laboratory
Find all cats in the cell I
Find all cats in the cell II
Find all cats in the cell IV
Find all cats in the dungeons
Find the castle map
Find the crystal ball