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.
Discover all areas of the map.
Speak to all of the spirit animals.
Find the dwellings of the rift cult.
Find the statue of crane.
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 statue of the fox.
Find the giant birdshrine.
Complete the Eventide Sanctuary.
Get some Lambaby love.
Find the statue of the deer.
Find the Crab Island.
Step into the well.
Escape the collapsing cave.