5e PHB page 24: "Drow grow up believing that surface-dwelling races are inferior, worthless except as slaves."
5e PHB page 40: "Other scars, though, mark an ore or half-ore as a former slave or a disgraced exile."
5e PHB page 94: "When their target-a notorious slaver-passes the alleyway, the accomplice cries out, the slaver comes to investigate, and the assassin's blade cuts his throat before he can make a sound."
5e DMG Page 19: "The cities of High port and Suderham in the Greyhawk campaign setting are satrapies controlled by agents of a vicious gang of marauders known as the Slave Lords."
5e DMG page 54: "The largest cavern beneath the mountains, called the Great Dismal Delve or the Sevenfold Mazework, is home to the capital city of the dao, the City of Jewels. The dao take great pride in their wealth and send teams of slaves across the plane in search of new veins of ore and gemstones to exploit."
5e DMG page 56: "The heart of the city is the towering Charcoal Palace, where the tyrannical sultan of the efreet reigns supreme, surrounded by efreet nobles and a host of slaves, guardians, and sycophants."
5e DMG page 100: "Details bring a dungeon setting's personality to life. Great bearded faces might be carved on the doors of a dwarven stronghold and might be defaced by the gnolls who live there now. Spiderweb decorations, torture chambers, and slave pens might be common features in a vault built by drow, telling something about that location and its occupants."
5e DMG page 101: "And all the while, a hidden cell of draw scouts watches and plots to slay the mind flayers, then enslave whatever creatures are left."
DMG page 113: "18 Hidden slavers' den"
DMG page 225: "Each orb contains the essence of an evil dragon, a presence that resents any attempt to coax magic from it. Those lacking in force of personality might find themselves enslaved to an orb."
5e Acquisitions Inc pages 123: "Friedson is a North lander wh o has pushed his crew to more and more dangerous and despicable deeds in recent months. He has even talked about taking up full-on piracy and slave trading to earn extra coin, and the (mostly) good souls aboard the Tortured Tortle are looking for a new way to make a living."
5e Eberron-Rising From the Last War page 24: "When humans first came to Khorvaire, they enslaved many goblins and built their cities on the foundations of Dhakaani ruins. Galifar ended the practice of slavery, and these goblins are now citizens of the Five Nations."
5e Eberron-Rising From the Last War page 112: "Most of the Cyran population fled the goblin uprising, and those who remained were killed or enslaved." and "Lhesh Haruuc has abolished slavery in Rhukaan Draal, but some of clan lords continue this practice."
5e Eberron-Rising From the Last War page 139: "This story bears at least some truth. The elves were once slaves of the ancient giants, and the dragons dideradicate the civilizations of Xen'drik."
5e Eberron-Rising From the Last War page 198: "The kobold lord Kethelrax has laid claim to Shaarat Kol in the south of Droaam and leads host of kobolds and goblins-creatures that have been traditionally enslaved and oppressed by the larger and more powerful inhabitants of the region."
5e Ravnica page 221: "These creations become thrulls, obedient slaves that serve in a variety of menial roles: laborers, messengers, beasts of burden, and even fashion accessories for the elite."
I can go on and on, including Tasha's and Mordenkainen's Monsters of the Multiverse. 5e has slavery everywhere, including several instances of ongoing legalized slavery. Dark Sun won't even stand out really.