Here is the full list of all 20 Unforgotten achievements.
Finish the game escaping from the weird settlement.
Find a mysterious altar in the forest and rest near it.
Get a potion from a chest.
Break a chest in an attempt to open it.
Find an old photograph in the kitchen.
Peek at the old shaman.
Quarrel with Egor to get imprisoned.
Persuade the man with deer skin not to fight to the death.
Craft a stone knife while being held captive.
Persuade the villagers to free the man with deer skin.
Finish the game becoming a ritual sacrifice.
Complete the prologue to wake up in a strange house.
Obtain an amulet fighting with Egor.
Start a new day in the weird settlement.
Solve a puzzle in the mine and obtain Egor's knife.
Seduce a girl in a dark cloak.
Receive a gift from the mysterious girl.
Win a fight with the man with deer skin.
Knife Egor.
Finish the game as the cult leader.