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.
Completed the game.
Speak to all of the spirit animals.
Complete the Archives.
Find the dwellings of the rift cult.
Find the ancient battlefield.
Find the giant birdshrine.
Find the chiseled stone map.
Find the statue of crane.
Step into the well.
Find the Crab Island.
Find the Ancient Llamba.
Complete the Monastery.
Discover all areas of the map.
Find the bones of an old beast.
Complete the Eventide Sanctuary.
Get some Lambaby love.
Find the statue of the fox.
Find the statue of the deer.
Escape the collapsing cave.