So I did all the achievements to unlock them on horde. Then I logged into my level 55 alliance character but the recruitment quest won’t pop the banner that’s in stormwind embassy is all green but still no quest
You’ll need to unlock Mechagon on your Alliance character if you haven’t already. You should be able to get Fame Waits for Gnome One from Gila Crosswires in the Embassy (which lets you skip Naz’jatar.) Give her a few seconds to phase in if you don’t see her immediately.
I just checked and can see Gila (she’s near the door) on a level 51 that has not unlocked BfA world quests, but has done the BfA intro. So, if you aren’t seeing her, it may be worth doing the BfA intro on the character to see if that helps.