The universe is expanding, not only at a constant speed, but it is accelerating.
Light is considered normal matter, so when light travels through dark matter, it is bent and distorted because the dark matter repellent properties of gravity.
The universe could be accelerating its expansion because of timescape cosmology.
An experiment by Wiltshire produced an explanation from an experiment to prove this...
Because of the lumpy structure of the universe, timescape cosmology contains variations in the effects of gravity causing the universe to accelerate its expansion over time.
This has nothing to do with dark matter and does not contain any amount of dark matter within it.
Another problem is that when scientists use the Type 1a supernovae to measure the distance of things in space through dark matter, they are measuring incorrectly because Type I a supernovae is not consistent. It can vary depending on its mass.