The following is a conversion of the 1991 Dark Sun boxed set to 5E rules. It is heavily focused on early TSR source material essentially ignoring the Prism Pentad metaplot that I thought ruined the setting along with some of the later source books that were written by freelancers whle TSR was collapsing and the original creators had moved onto other project. My conversion is fosused on the themes of the original Dark Sun.
Survival. Water is rare on Dark Sun outside the main cities. It is hot and the wastes of Athas are deadly.
Environment. The world has been ravaged by sorcery. The PCs can ruin the world or try to repair it.
Slavery. Slavery is widepread, how the PC respond is up to them but heroic PCs likely want to help them.
Brutality. Athas is an unfair world and the environment is harsh. PC can arbitrarily be put to death or enslaved in the cities which are ruled by Sorcerer Kings and their servants the Templars. In the wild getting baked to death by the sun, eaten or choking on silt are all hazards and risks.
Magic is hard. Defilers have ravaged Athas and being identified as a wizard (defiler or preserver) can be a death sentence. Knowledge is rare about the finer points of magic and one has to resort to black markets to get things like spell books. A smart wizard hides their power or passes it off as psionics (hard to do as a Defiler).
Everything is psionic. In comparison to magic psionics is easy. Every PC has a wild talent. That cactus in the desert could actually be psionic.
Lack of metal. Metal on Athas is rare and there is 1 gold mine and 1 source of iron in the Tyr region. Metal goods cost 100 times the equivalent in the PHB. A Sorcerer King can afford several suits of plate armor or can rebuild the walls of their city.