What specific process marks the end of sustained heat generation via fusion in a star's lifecycle?

Creating elements heavier than iron consumes energy rather than releasing it

While stars evolve through several stages of nucleosynthesis, converting progressively heavier elements in their core, the long-term, sustained energy production ceases when the stellar core begins forging elements heavier than iron. Fusion reactions up to iron release net energy because the binding energy per nucleon increases as lighter elements combine to form elements nearer iron's atomic structure. However, once the core begins fusing elements heavier than iron, the process becomes endothermic; it requires an input of energy from the star rather than releasing energy into it. This shift marks the end of the fusion furnace as a sustainable power source, leading rapidly toward the star's final catastrophic demise as internal support pressure vanishes.