This is some interesting speculation, and I applaud the researchers who think of things like this to look for.
I still estimate that by the time a civilization has planetary-scale engineering capability, that they won't need to make things like starshades.
If you have molecular nanotechnology, you can either adapt yourselves to whatever location you find, or just skip the biological body business, and directly upload your consciousness to a computer network.
The 2nd option is far more mass and energy efficient to support large numbers of sophonts, and I expect that any civilization to endure long enough will have the majority of its population living online instead of offline. If that even ends up being a thing, and they all don't just merge into a single entity (going in the direction of Star Trek's borg).
I always think of the "they're made of meat" story when considering this [1].
How do we even know what life looks like out there? Or what it has turned itself into in order to survive, travel and spread? Or even what it started out as?
We can't even talk with dolphins, even though we have a very recent evolutionary common ancestor. They're sentient life, tool-users, do we think they'd build a starshade to solve this problem? Shame we can't ask them, or understand their answer.
We know trees are alive, we know they communicate with each other. We don't think they're sentient. But how would we know? What would a sentient tree do differently from a non-sentient tree? What would a sentient tree do about the sun getting hotter?
Even if they started out like us, the evolutionary responses to living on other planets will change them. We're adapted to the conditions on Earth. If we live on other planets with different conditions then we will adapt, because that's what we do. We don't know how far those changes will go, because all the life we've ever seen has been adapted to Earth. Maybe high-gravity humans are less like sci-fi dwarves and more like Pratchett trolls.
We seem to be expecting sentient life out there to resemble us and have similar solutions for their problems. This seems dumb to me.
Maybe, but this conversation always inevitably ends up in this territory ("But what if aliens are crystals?"). And sure, we can't know. But we're going to have to make some assumptions, and we all do live in one universe, with a common constituent set of physical laws. Aliens that build spaceships probably also have airplanes and an internet. I don't think it's dumb to speculate with some reasonable assumptions, and while I appreciate that this conclusion always comes up and is not wrong, it's uninteresting.
We could make starshades today if we made it a priority. It would take a shade roughly only about 0.09% the size of the cross-section of the Earth to change the climate as much as all of our CO2 emissions. That's only a roughly 200km in radius shade. If we were spending, say, a trillion dollars a year (1.3% of global GDP, a sum less than what is spent on many other things) we could almost certainly build and launch such a structure in at most a few decades.
I still estimate that by the time a civilization has planetary-scale engineering capability, that they won't need to make things like starshades.
If you have molecular nanotechnology, you can either adapt yourselves to whatever location you find, or just skip the biological body business, and directly upload your consciousness to a computer network.
The 2nd option is far more mass and energy efficient to support large numbers of sophonts, and I expect that any civilization to endure long enough will have the majority of its population living online instead of offline. If that even ends up being a thing, and they all don't just merge into a single entity (going in the direction of Star Trek's borg).