Mysteries of the Maw in WoW is a new quest part of the Korthian content added in Patch 9.1.
Mysteries of the Maw WoW: Everything You Need to Know
Ve'nari of The Maw has you begin Mysteries of the Maw, located where she always is at Ve'nari's Refuge. Mysteries of the Maw is an essential quest to complete in order to gain access to the new zone added in 9.1, Korthia.
After accepting Mysteries of the Maw, use the Animaflow Teleporter just behind Ve'nari. She will follow right behind you as some dialogue plays. After landing from the Animaflow Teleporter, follow Ve'nari in her shroud of invisibility as your trek through the dangerous Beastwarrens.
Stay close to Ve'nari, the Beastwarrens are super dangerous, and if you leave Ve'nari's protective shroud, the mobs around you will aggro, likely killing you if you don't leave immediately.
Continue with Ve'nari through the southern portion of The Maw and you will eventually reach the portal to Korthia. You can now pick up the quest from Ve'nari titled Korthia, the City of Secrets, and continue your journey into all the new 9.1 content!