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.
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 ancient battlefield.
Find the bones of an old beast.
Find the statue of the deer.
Complete the Archives.
Find the statue of the fox.
Find the chiseled stone map.
Find the giant birdshrine.
Find the statue of crane.
Find the Crab Island.
Complete the Eventide Sanctuary.
Get some Lambaby love.
Step into the well.
Escape the collapsing cave.