Yaarel
🇮🇱 🇺🇦 He-Mage
The 5.5 elimination of "half" species and the use of the term "species", confirms Elf and Human cannot reproduce children together.Probably best not say what is or is not genetically impossible in an imaginary elf game. Stories are filled with shapechanged dragons siring children with dragon blood.
3e had whole prestige classes for growing up as a half dragon.
Any lore where there is mixed ancestry was accomplished by means of magic. Typically, the Elf parent shapeshifted into a Human, and the children are Human. Often the children also inherit a nonbiological magical capacity from the Elf parent.