In Stanisław Lem's Fiasco, the nature of the inhabitants of the alien planet is never directly revealed, only hinted at.
On the forums there is some amount of speculation about it, the most common ideas are:
they are colonies of ant-like small creatures. The mounds are something like ant or termite colonies (hinted by a story-within-a-story about the "god of the termites")
similarly to the previous theory, they are microscopic beings.
they retreated below the surface and are living in some kind of virtual reality, they lost all direct sensory connection with the outside world and are maintained by machines, so there is no nanotechnological cold war, there are just robots who maintain the planet. The ice ring around the planet is in a bad shape of disrepair because no one needs it, as the inhabitants are devolved into huge blobs (the mounds) fed by nanobots, and no agriculture or other surface activity is needed.
In-universe nothing more can be known, as
the planet is destroyed at the end of the book, and the only person who understood what they are, dies before he can tell it to the crew.
Can there be any proof, evidence, or stronger hint about the true nature of the quintans? For example, did the author ever told an answer or at least some clues on an interview, etc?