>>11195356One look at the linear decline of fertility rates as earthbound societies increase in intelligence and technological prowess should tell you that the civilizations most capable of building Dyson spheres, ringworlds, etc are likely those with the least need whatsoever for them.
What's far more likely is that there are a handful of civilizations in the galaxy at a given moment that are at various stages along the path to becoming Alita/Cowboy Bebop/Firefly-style system-spanning civilizations that live out their lives in a stagnant, spacebound version of the 18th century age of sail, only with planets instead of nations, before they either kill each other off, exhaust their resources, turn inward or become stationary AI or something like the matrix.
Interstellar travel is probably the great filter, and the largest that most civilizations probably ever get is becoming Battlestar Galactica-style collections of a handful of star systems that are close enough to each other to sustain an Avatar-style interstellar economy based on relativistic sublight travel, before they succumb to the same fates as the solar system-level civs.
I'd also bet that when the interplanetary or interstellar economy shuts down, it probably leaves a few leftover planetbound civs that are locked in a set of Westeros/Middle Earth-style technological stasis that ranges anywhere from the stone age to where we are today.
