This guy Crecganford on Youtube made a searchable database of the mythology index https://www.mythologydatabase.com/ , but it looks like he put a login requirement since the last time I looked it up. Creating an account is free, and I find this on the "Achilles' heel" motif :

https://www.mythologydatabase.com/get_motifs.php?myth=l15a1

Caucasus - Asia Minor. (Cite)

Kabardian people [sledges strive to destroy too strong Sosruko; offer him to roll a wheel up the mountain; push him with his head; S. performs everything; the old woman says that when S. was taken out of the stone womb that gave birth to him, the blacksmith grabbed his thigh with forceps, it became covered with bone and became vulnerable; sledges offer to roll the wheel with his thigh; the wheel crushed his thigh, S. died]: Lopatinsky 1891a:46;

Wikipedia's page for Sosruko points to this http://iccs.synthasite.com/nart-epos.php which calls him Sosriqwe and presents him as a variation of Prometheus and Loki, a trickster who steals fire from the gods and get punished for it.

Could it be that it isn't an actual ancient myth, but a modern(ish) story that reinterprets the myth of Achilles in the context of a different culture? Because that is suspiciously similar.