Here is the full list of all 20 AER - there are Memories of Old achievements. It takes around 3-4 hours to unlock all of the achievements on Windows.
Find Erin when she's gone.
Step into the well.
Completed the game.
Complete the Monastery.
Find the Ancient Llamba.
Discover all areas of the map.
Speak to all of the spirit animals.
Find the statue of the fox.
Find the giant birdshrine.
Find the chiseled stone map.
Find the Crab Island.
Find the bones of an old beast.
Find the dwellings of the rift cult.
Find the ancient battlefield.
Complete the Archives.
Find the statue of crane.
Find the statue of the deer.
Complete the Eventide Sanctuary.
Get some Lambaby love.
Escape the collapsing cave.