Here is the full list of all 28 The Last Birdling achievements.
Unlocked ending 4.
Finished chapter 21.
Finished chapter 20.
Finished chapter 19.
Finished chapter 18.
Finished chapter 17.
Finished chapter 16.
Finished chapter 15.
Finished chapter 14.
Finished chapter 13.
Finished chapter 12.
Finished chapter 11.
Finished chapter 10.
Finished chapter 9.
Finished chapter 8.
Finished chapter 7.
Finished chapter 6.
Finished chapter 5.
Finished chapter 4.
Finished chapter 3.
Finished chapter 2.
Finished chapter 1.
Started a new game.
Unlocked ending 1.
Unlocked ending 2.
Unlocked ending 3.
Unlocked ending 5.
Obtained all endings