What evolutionary stage prevents a star from obeying the standard Mass-Luminosity Relation?

Evolved off the main sequence (e.g., red giant or white dwarf)

The validity of the Mass-Luminosity Relation, often expressed as $L imes M^{3.5}$, is fundamentally tied to the star being in a specific, stable evolutionary phase: the main sequence. This phase represents the long period where the star is actively fusing hydrogen into helium in its core, balancing the inward pull of gravity with the outward pressure from fusion—a state of hydrostatic equilibrium. When a star exhausts its core hydrogen supply and evolves away from this equilibrium, entering phases such as becoming a red giant or eventually shrinking down to a white dwarf, its internal structure and energy generation mechanisms change radically. Consequently, the relationship between its current luminosity and its total mass no longer conforms to the standard main-sequence scaling law, rendering any mass estimate derived using that specific empirical relationship inaccurate for these evolved objects.