Homosexuality is not genetic.
Interesting.
Where do traits that aren't genetic come from then?
It's complicated. The most compelling theory is that several genes might have a bit of an influence paired with the hormonal conditions in the womb. Here's an overview:
https://en.wikipedia.org/wiki/Epigenetic_theories_of_homosex...
A variety of sources[1].
1. https://pmc.ncbi.nlm.nih.gov/articles/PMC4262890/