During the patch 9.2 announcement preview, Maria Hamilton, the Lead Quest Designer mentions that Spider mounts will now be able to fly in World of Warcraft while showing a video of a new mount flying in Zereth Mortis, which made players question if they would be able to fly in this new zone.
In an interview by Millenium, with Ion Hazzikostas and Sara Wons, the team was asked if flying was going to be a part of the new zone and Sara Wons Confirmed it will be unlocked as part of the new Cypher of the First Ones System.
"Yes, in the end you will have the flight in this area thanks to the decryption system. So you will have access to that! " Wons Says.
Due to the original interview being in French this answer is translated, but we now know that flying is possible in the realm of the First Ones.
Flying Will Be Unlocked In Zereth Mortis During Patch 9.2 Eternity's End
As Eternity's End is the final content patch of the Shadowlands, players were expecting to not fly in this new zone as some end game zones don't allow for it such as the Timeless Isle and Argus.
This is good news for players especially as Blizzard has confirmed that the zone will be on the larger side of zones added during a later content patch.
Players will also unlock flying by completing content that they will need to complete anyway, through the Cypher of the First Ones system.
Players will likely need to unlock Shadowlands Pathfinder, to fly in Zereth Mortis, although we will know more once the PTR is live, which is expected over the next few weeks.