In the back story of Wonder Woman 1984, Diana has been on her own for quite some time. She has been secretly saving people and trying to uphold justice. Her longing for Steve Trevor is a big part of her emotional back story. As for the villains, Maxwell Lord is a con man who gets in over his head with a magical item. His desperation for success based on his past failures is part of his back story. The Cheetah was once Barbara Minerva, a woman who was envious of Diana's strength and beauty and through a series of events becomes the Cheetah, which is all part of the complex back story of the movie.
The back story involves Diana Prince still carrying the memories and values from her past. In this story, she has been living in the modern world since the events of the first movie. She's still a symbol of hope and justice. There are also elements related to the villains and their own back stories which tie into the overall plot of the movie.
Well, the back story in Wonder Woman 1984 has Diana in a world that has changed a lot since the 1910s or so. She has seen wars come and go. Her back story also includes her love for Steve Trevor which is rekindled in a rather unique way in this movie. The antagonists have their own back stories too. Maxwell Lord wants power and wealth and his past experiences drive his actions. The Cheetah also has her own origin story that is connected to Diana in some complex ways.