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