A Dyson sphere is a hypothetical megastructure that encompasses a star and captures a large percentage of its power output. The concept is a thought experiment that attempts to imagine how a spacefaring civilization would meet its energy requirements once those requirements exceed what can be generated from the home planet’s resources alone. Because only a tiny fraction of a star’s energy emissions reaches the surface of any orbiting planet, building structures encircling a star would enable a civilization to harvest far more energy.
Would recommend Orion’s Arm for “theoretical” but fiction takes on structures like this:
https://www.orionsarm.com/eg-article/5067d430e6021
That article is not comprehensive either, their universe is quite expansive.
Two of my favorites may be “W-brains,” computing structures with very carefully arranged wormhole pairs serving as data buses to overcome the latency of communicating at such scale, and “neural stars,” another take which is a computational structure inside a neutron star sized volume/mass (again, to overcome latency issues).
There are much smaller megastructures too, depending on where in the timeline you are looking.
Is this like the SCP foundation stories but for space opera science fiction?
Precisely.
And it’s a “hard” sci fi universe rooted in theoretically possible physics. No FTL or causality violations.