I had to go to the Tree with a full bar, after lvl 50, before getting a sigil drop. Then sigils dropped in that Nightmare dungeon but not in open world nor in Helltide.
Sigil vendor options are still greyed out (lvl 54)
I am also experiencing this issue in my seasonal character. I’m in T3 and have completed multiple NM dungeons, but I never got the sigil crafting quest and the tabs are greyed out at the Occultist.
this is still an issue, im into world tier 4 and it is still not unlocked, done numerous nightmare dungeons , tried logging out of battlenet, switching tiers back and forth, updating game, verifying integrity, and its still not working (in seasonal btw)
As you kill monsters and progress through the Tier 1 Nightmare Dungeon, you are likely to find a Tier 2 Nightmare Sigil. If you do not, run any Tier 1 Nightmare Sigils you acquired in that dungeon to try again. You can also reliably acquire additional Tier 1 Sigils through the Tree of Whispers.
Run a Tier 2 Nightmare Dungeon or Dungeons to acquire a Tier 3 Nightmare Sigil.
Once you acquire a Tier 3 Nightmare Sigil, complete that Dungeon to unlock Sigil Crafting!