I have no doubt that I'm about to be wrong, but...

What if dark matter + space/time = gravity and space/time without dark matter = freedom of movement without restriction which = expansion.

I think of it as dark matter somehow activates space/time, would that mean there's region's of space in which relativity does not apply?

Just a brain fart, but I'd love to know why I'm wrong, preferably in a language I sort of understand...

The term 'dark' is a descriptor signifying we can observe the effects, but we don't know the cause.

The effects are accelerating expansion and anomalous gravitational effects that don't fit the Newtonian model.
These effects indicate an unknown energy, and an unknown mass other than the visible, as the causes.

So, in really simple terms, unknown energy = dark energy, and, unknown mass = dark matter.

We do know that matter, with the property of mass, couples with space-time as per GR, and that affects expansion ( no expansion where gravity, or non-trivial space-time curvature, binds masses together ) but I don't see how that equates to 'freedom of movement' or regions of space where relativity does not apply.