MCU Endgame isn't directly based on a specific single story arc. It's a culmination of multiple storylines and events from the entire Marvel Cinematic Universe.
MCU Endgame doesn't have a one-to-one correspondence with a particular story arc. Instead, it weaves together elements from various previous films to create a grand conclusion. It incorporates plot points and character developments from movies like Infinity War and earlier installments to form a complex and epic narrative.
The MCU Endgame isn't tied to a single defined story arc. It's a synthesis of multiple storylines that have been building up throughout the MCU. It brings together characters and plotlines from different films to deliver a satisfying and climactic ending.