Every NPC in Grommash Hold and their subsequent quests or functions are inaccessible to new players who completed Exile’s Reach. The reason for this (I am 100% sure) is they removed the quest that sends you to meet Sylvanas to start BfA content because you are now directed to Dragonflight. But they did not account for this when the change was made, and now any new Horde player has Sylvanas phasing out the entire hold. The ONLY thing I can think that might work is obtaining the Heart of Azeroth at 50. In the past, that has essentially forced BfA phasing issues to resolve. But I can’t report on that yet and I’m not sure I want to grind 12 more levels tonight to confirm. This is a really inexcusable bug.
Edit: Even this doesn’t fix it, as it has for other Orgrimmar phasing issues in the past. Blizzard has managed to completely bork the throne room for every new Horde player coming to the game, it’s been like this since the pre-patch, and nothing has been done about it.