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