Main Quests in Horizon Zero Dawn are essential missions. In order to continue the storyline and complete the game, the player has to complete Main Quests in the given sequence. There are a total of 22 Main Quests in Horizon Zero Dawn.
After completing the final Main Quest, The Face of Extinction, the game will reset to a state just prior to starting the penultimate quest, The Looming Shadow. Despite this, you will still keep any items or XP acquired during the final Main Quest.
All Main Quests in Horizon Zero Dawn