Space is a medium, as exemplified by the fact that light curves around massive objects, because the space is curved.
Space isn’t a medium because mediums have privileged frames of reference.
You’re talking about spacetime which is a field, not a medium.
Light is also not “stuff” - it’s electromagnetic radiation. It’s by the unprivileged intertial frame of reference that we define the speed of light. Light’s speed is the speed at which it travels unimpeded through the spacetime “field”. Additionally light does not accelerate or change speed in any way while traveling in that frame.
Unless you’re asking if light travels through things that are not the field known as the spacetime continuum in which case yes: light travels (and changes speed) through all sorts of materials. Like glass.
