Why is constant motion relative to absolute space undetectable in Newtonian physics?

In Newtonian physics, constant motion relative to absolute space is undetectable because the fundamental laws of mechanics, specifically Newton’s second law of motion ($F=ma$), are invariant under Galilean transformations.1

This invariance means that if the laws of motion hold true in one inertial frame of reference, they will hold true in any other frame moving at a constant velocity relative to the first. Because the acceleration of a body is identical when measured from any of these inertial frames, no mechanical experiment performed within a closed system can distinguish between being at rest in absolute space and moving at a constant velocity.12

Consequently, while Newtonian mechanics assumes the existence of absolute space as a fixed framework, the mathematical structure of the theory ensures that uniform motion relative to that framework remains empirically inaccessible. This principle of relativity led to the long-standing belief in theoretical physics that all fundamental laws must be invariant under such "boosts" between inertial frames.13