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