In the last few weeks I leveled some characters to level 40. Then you are eligible to do quests to unlock new races.
I found it time consuming to unlock the Kul Tiras Human, because I have to go to several areas of Kul Tiras. For the Dark Iron Dwarf I had to go to Blackrock Depths and to Molten Core. Unlocking the Zandalari Troll I could stay in the capital city of Zandalar. I didn’t have to travel anywhere.
I notice difference in the time and some difference in difficulty. Do you experience that as well? But there is no race until now, whose unlocking is so hard that I had to give up.
I think that Void Elf is the easiest (some quests in Ghostlands and that’s it). I also unlocked Nightborne.
It used to be a bit more time consuming having to do it, so at least you didn’t have to do all that stuff! If you haven’t done them before, it was to get to Exalted with certain factions and also complete story achievements.
I remembered that too. I wanted to play new races, but I had to meet high requirements. Except for one (maybe that race was added with The War Within), you must just talk to the Embassy in Orgrimmar (for new Horde races) or Stormwind (for new Alliance races) and follow the questline from there.
Since those requirements were dropped, except your char must be level 40 or higher, I unlocked one race after the other.