Yeah. Detrivores.

Carnivores eat other animals.

Herbivores eat plants.

Omnivores eat plants and animals.

Detrivores eat organic detritus, the remains and leavings of living things.

Modern human civilization is akin to being a detrivore (if you think of civilization as being a system organism), because it exists off the energy of fossil fuels, a finite, one time inheritance of concentrated detritus of living things pressure cooked inside the earth for millions of years.

As far as the civilization organism goes, it has one food source. One. Without that food source, the organism dies, even if it is a system organism rather than a biological organism.

All living things must eat or perish. A system organism is no different.

You may bring up solar or nuclear power. They will always depend upon fossil fuels to create. They could slow down the consumption of fossil fuels, but eventually fossil fuels will run out. When they do, the civilization organism will either adapt to a new energy source or starve. Simple physics. Simple biology.

The Egyptians and the Papuans were not part of a world economy supported by fossil fuels. Fossil fuels hadn't even been discovered yet with the Egyptians. The Papuans are still around but fossil fuels were not in such widespread use during the time period I believe you were referencing.

Collapse aware, or as you call them, catastrophic thinkers, have reckoned with the fact that we humans now exist as individuals but that we also exist as symbiots to another organism. A system organism that not many of us can survive without anymore.

What happens to your gut microflora when you die?

They die too, right? A few may escape, but the majority of anything living within you dies when you die.

That wasn't true of the Egyptian civilization, or even other collapsed civilizations. For one, they had somewhere else to go, where we humans have already populated the entire planet. Meaningful space travel is a fantasy at this point, regardless of what Elon Musk has been smoking. That's not going to change anytime soon. Certainly not before we hit climate tipping points. Secondly, their civilizations weren't detrivores.