Dormammu is the dark being trying to destroy the universe in Doctor Strange. Dr Strange uses the Time Stone to keep Dormammu away, this being is referenced in Avengers: Endgame, when the Ancient One says she can't lose the protection of her realm and is convinced by the Hulk to release the stone.
Back to the beginning of Endgame, once Thanos destroys the Stones, Dormammu should swoop in for the obliteration of the Earth. Why didn't it happen, did Dr Strange destroy Dormammu?
against the forces of darknessin plural which means there are other threads than Dormammu. Also the sorcerer did not know that Dr.Strange gave away the stone, there is also no indication that she knew about the attack of Dormammu either. This is simply a plot hole.