What are the possible final stellar states following a core collapse supernova of a massive star?

Neutron Star or Black Hole.

When a massive star, exceeding approximately eight solar masses, exhausts its fusion capability by forming an iron core, the resulting core collapse leads to one of two extremely dense final states, depending on the remnant's mass after the initial implosion. If the core remnant's mass falls within a certain range after the collapse and rebound shockwave, the immense pressure compresses the matter to nuclear density, creating a neutron star. However, if the mass of the collapsing core is sufficiently large even after some material is ejected, the gravitational force will overwhelm all internal resistance, causing the core to collapse indefinitely, resulting in the formation of a black hole. Both outcomes follow the violent core-collapse mechanism.