The Duergar is the only non-core dwarf that we’ve seen in 5e, and I suppose it’s no surprise that they were republished in Monsters of the Multiverse alongside the Deep Gnome.
Like other races with innate spellcaster, the Duergar’s innate spellcasting now allows players to select the spellcasting ability and re-cast the spells with spell slots. Unlike other races, the Duergar’s innate spells can only target the caster, limiting their usefulness.
The changes to the Duergar also deviate from the core dwarf traits, removing both their racial weapon proficiencies and the iconic Stonecunning. I don’t know what this tells us about the future, but I’m curious to see what happens in the “next evolution” of the game.