- Unlocked flying in Legion, but can't fly on Argus.
- Is there a quest to enable flying on Argus?
You can't fly anywhere on Argus, even if you unlocked flying in Legion zones by completing Broken Isles Pathfinder, Part Two. This is a deliberate design decision by the World of Warcraft team.
While there are no plans to allow flying in the future, you can complete an achievement to increase your mount speed on Argus.