The Darkness subclass introduced in Destiny 2: Lightfall was Strand.
Strand is a Darkness-based subclass built around manipulating a psychic web that connects all living things. Guardians discover it while defending Neomuna, where threads of this power run through the city and its connection to the Veil. Unlike a conventional elemental weapon, Strand is presented as a force of consciousness, connection, and movement.
Its signature mobility ability is the grappling hook, which lets Guardians latch onto objects, enemies, or floating Strand points. The subclass also uses suspend, sever, and unravel effects, giving its three Guardian classes different ways to control the battlefield. Titans become Berserkers, Hunters become Threadrunners, and Warlocks become Broodweavers.
The main confusion is Stasis. Stasis was also a Darkness subclass, but it arrived earlier with Beyond Light in 2020. Strand debuted with Lightfall in 2023. Void and Solar are older Light subclasses, so neither qualifies as the new Darkness power associated with the expansion.