Stargate Atlantis ended after five seasons, but there are currently two storylines that tell the tale of what happened afterwards.
The first storyline was the eight novel series Stargate Atlantis: Legacy, published from 2010 to 2015. In this series, Atlantis returns to the Pegasus Galaxy only to find that all the Wraith are uniting under a single queen who called herself "Death"*.
More recently is the comic series Stargate Atlantis: Back to Pegasus, published in 2016. In this series, Atlantis also returns to the Pegasus Galaxy, but instead they find the mysterious alien species first encountered in a parallel dimension in the episode The Daedalus Variations.
These two series are mutually exclusive, since they both tell different stories of why Atlantis returned to the Pegasus Galaxy and what happened when they arrived. Have either of these been deemed to be official canon continuations of the show?
The Stargate Wiki is no help, since it says that both storylines are canon, which they can't be.
* Personally, I found the idea of Wraith giving themselves names to be ridiculous, since they were all nameless in the show (except for the ones that the Atlantis team named, like Todd). But that's beside the point.