It appears you have to be level 10 to do that. I'm only level 5. Oh well. I'm just not a dedicated gamer. Although considering how many hours I'm putting in to get the Civ 6 achievements, I'm pretty dedicated.
So far my rarest achievement is Selfie. It's not hard to get, surprised it's not a higher percentage. Third Crusade is my 2nd rarest achievement at 0.5%. That one felt more like an achievement, after painstakingly and annoyingly moving an entire army 1 unit per tile all the way across the continent to get to Jeruselem. Would have been faster to just keep restarting games until I found Jeruselum next to me, but I haven't been getting my achievements that way. I have been playing full games (Epic speed). I'm still less than halfway through the civilizations because of it.