WoW Shadowlands 9.1 release date has yet to be officially revealed. Players are anticipating the first Shadowlands update as Blizzard has confirmed that flying will be coming to the Shadowlands zones in 9.1.
WoW Shadowlands 9.1 Release Date: Everything We Know
The details about flying in Shadowlands are mostly unknown, but there are a few key changes since Battle for Azeroth that are worth noting for other zones. You won't need the Pathfinder achievements to fly in Warlord of Draenor or Legion zones anymore, but you will need Expert Riding. In Battle of Azeroth zones, you'll still need the Pathfinder achievements.
With all of these changes to flying, players have been speculating how this will affect the zones in Shadowlands. Not much is known except that Covenant Renown will be an important factor in unlocking flying.
In addition to flying, it's expected for 9.1 to bring a few new zones and expand upon some lore found in Shadowlands flavor text.
As for timing, there are no official news as to when Shadowlands 9.1 will release. Looking back to Battle for Azeroth, it took four months for the first major content update to release. Shadowlands released in October 2020, so we could expect 9.1 to release some time near February 2021.