According to Ra, ambrosia is the food of 4th density

[Dtris]

Ambrosia is the name given to the food of the gods in Greek and Roman mythology. It was believed that by ingesting ambrosia it would lengthen the life, heal physical ailments, and could even make you a demigod.

My interpretation of that passage is that Ra was hinting that past myths of ambrosia as the food of the gods were in reference to 5th density other selves who interacted with ancient humans. The ambrosia itself is not something that can be made by humans as it is fifth density food.