Gravity, despite not being considered a force in the traditional sense according to Einstein's theory of general relativity, is responsible for the phenomenon we perceive as "being held down." Instead of being viewed as a force, gravity is described as the curvature of spacetime caused by massive objects such as the Earth.
According to Einstein's theory, objects with mass cause spacetime to curve, and other objects moving through this curved spacetime will follow curved paths. In the case of Earth, its mass creates a curvature in spacetime around it. As a result, when you stand on the surface of the Earth, you are actually following a curved path through this curved spacetime.
It is this curvature that determines the motion of objects in the vicinity of Earth. Instead of a force pulling you down, you are simply following the natural path dictated by the curvature of spacetime caused by Earth's mass. This phenomenon is often referred to as "gravity," even though it is not considered a force in the classical sense.