Not that i’m not upset also, but please read.
Quote Bliz:
Before you unfurl your wings, you must progress through the newest chapters within your covenant campaign, specifically early into “The Last Sigil” (chapter 12 of the covenant campaign). This chapter unlocks when you reach Renown Level 44, accessible within the second week of Chains of Domination.
Rank 45 gets you the mount, 44 gets you flying.