A new action RPG set in Nickelodeon's Avatar franchise is in development, but Aang won't be the main character.

The Avatar Legends multimedia universe is expanding with a brand new AAA game, sources have revealed to IGN. The project will see Paramount Game Studios team up with Saber Interactive, the label behind Warhammer 40K: Space Marine 2, World War Z, and the Evil Dead video game.
No official photos, images, or teasers were revealed for the game, but it was revealed that the interactive adventure will be centered around an entirely new and original Avatar--meaning Aang won't be the star. Paramount told IGN that gamers "can expect to be immersed in a vibrant world, master all four elements, engage in dynamic combat alongside companions, and experience the challenges and decisions that come with being the keeper of balance in the world."
There's also a few snippets of info from Paramount and Saber Interactive.
Paramount:
"We know loyal fans of Avatar: The Last Airbender have been eager for more stories that bring them into the universe of the show, and through gaming, we're able to expand the world-building and allow fans to experience the new content in a completely immersive way," said Doug Rosen, SVP, Games and Emerging Media at Paramount.
"Saber Interactive has a proven track record in bringing IP-based games to life, and we are excited to co-fund this AAA title alongside them and let fans experience this world first-hand."
Saber Interactive:
"At Saber, we are all truly fans of the IP we work with. Our team members are some of the most devoted, passionate creatives out there and it's an honor to join forces with Avatar Studios and Paramount Games to further expand the Avatar Legends universe in video games. This unique co-fund structure is a result of our ever-expanding collaboration with Paramount, which started over a decade ago with WWZ, and we're excited for all that's on the horizon," said Josh Austin, Head of IP Development & Licensing, Saber Interactive.