Boss fight
Once geared up, head into the Dark Aether Nexus. Follow the purple beams to a wall with a pedestal. Interact with the pedestal and a bride will appear.
Interact with the Sential Artifact at the center of the arena. All players will need to vote to continue. Unlike the recent boss fights with three phases, this is a tedious boss fight with about ten phases. Each phase will provide you with a Max Ammo power-up.
In the first phase, just survive and avoid the red beam shot from the Sentinel Artifact. Once the Sentinel Artifact turns purple, it becomes vulnerable and you can shoot it. Group Aether Shroud strat works well here.
Each phase thereafter will progressively add more lasers. You just want to stay alive and deal damage once the Sentinel Artifact goes purple.
Just keep working through the phases, and you’ll get a final cutscene and rewards for completing this story quest.