To achieve Twilight Beckons you need to play the story all the way up to the end in the 3rd and final fight between Kratos & Atreaus V Baldur. You will then need to proceed to defeat Baldur. Note that in this fight Baldur will transform between fire and ice elements, requiring you to switch between your blades of chaos and leviathan axe to be able to deal damage to Baldur. Upon defeating Baldur, Twilight Beckons will be unlocked.