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