After extensive research, I have found that there is no unifying creation myth for humans. The most I got from the origins of humanity is that we were one of the 5 original creator races that inhabited the ancient world, alongside the Aearee (Bird People), the Batrachi (Amphibian People), the Sarrukh (Lizard People) and the Fey. All the other races who came to Toril/Abeir was the result of gods placing them thereafter they were created.
I also read a legend that apparently when Asmodeus was still an angel he was the angel of a god known as He Who Was, who reportedly created humans, then Asmodeus killed him during the Dawn War and we've been up for grabs ever since. Again hard to tell the truth with Asmodeus.
I wonder if this why only Humans of all the mortal races are the ones who have managed to obtain divinity/godhood in some form or other as a handout to level the playing field. Still interesting topic.
