What initial mass separates stars into Red Giants versus Red Supergiants?

Red Supergiants usually start with masses exceeding 8 to 20 times the mass of the Sun.

The fundamental distinction between a red giant and a red supergiant is intrinsically linked to the star's birth mass. Stars that begin their lives with masses relatively low, typically up to around 8 solar masses, follow the evolutionary path of a red giant. Conversely, red supergiants are stellar behemoths originating from stars that were significantly more massive at formation, usually exceeding 8 to 20 times the mass of the Sun. This greater initial mass dictates the physics of their later lives, allowing for the necessary core pressures and temperatures required to fuse heavier elements far beyond what their smaller counterparts can achieve, leading them down a path toward a far more catastrophic end.