When astronomers talk about cosmological-scale observations to the press, they don’t use proper distance or comoving distance,
they use lookback time as a measure of distance, like we see at this NASA page:
“Current observations suggest that the Universe is about 13.7 billion years old. We know that light takes time to travel, so that if we observe an object that is 13 billion light years away, then that light has been traveling towards us for 13 billion years. Essentially, we are seeing that object as it appeared 13 billion years ago.”
The Cosmic Distance Scale
"Suppose we use the parsec definition above. That is, based upon the light we currently see, how far away is a quasar with redshift z = 6? Another way to say this would be "How far away was the quasar when the light left it?" This turns out to be about 1.2 billion parsecs. It's tempting to convert this to light years, and thus say it was about 3.9 billion light years away, but this is misleading. Because the cosmos was expanding as the light traveled to us, it actually took the light about 12.8 billion years to reach us.
So its light travel time distance is actually 12.8 billion light years. This is the most common "distance" used, since it's easy to compare with the age of the light."
How We Define Distance In An Expanding Universe
Otherwise they'd have to specify either A.) the distance at the time the light was emitted, or B.) the distance to the object now in comoving coordinates. So instead they use the time-of-flight, which is the lookback time, because in this example we're seeing the object as it was 3 billion years ago, i.e. the light has traveled a distance of 3 billion light-years. That's a lot easier than trying to explain either the distance to the object when the light was emitted, which was closer than it is now, or the comoving distance, which we can only infer, and which would only confuse people because the most distant objects are presently much further away in light-years than the age of the universe.
This is why most astronomers grit their teeth over the fact that pop science writers refuse to use the cosmological redshift factor
z instead using lookback time as a measure of distance: the redshift is the only real observable, and any distance scale is only a derivative of that.
No, lol - "most astrophysicists" don't expect Dyson spheres to exist.
The engineering issues are enormous and any civilization capable of building such a monstrous thing would've produced their own fusion reactors long before that point in their technological evolution...or probably found an altogether more useful source of energy than fusion.