|underground on an alien world|
The WhatIf Channel presents the little short, “What If We Found Earth 2.0”? There was a series called this ("Earth 2") in the 1990s with Anthony Sabato and an underground civilization of humanoids.
It’s likely to be somewhat larger than Earth and near a K star or possibly mature red dwarf (no longer flaring), and tidally locked.
But it would take many generations reproducing on a closed O’Neill-like spaceship with authoritarian politics to get there.
The short had an annoying long advertorial by NetSuite in the middle.
At the end, the video takes another look at Titan.
You can also watch “What If We Discover Life After Death?” on the same channel. It does explain the Greyson scale of 1983, and the syncing of brain to heart and nervous systems during death.