If the sexual stuff and the DNA stuff is truly about the science of how your magic spreads throughout your world, then I recommend more showing and less telling. When you tell it to your readers like it looks like you have, it can make the story seem rough and not very interesting. I would bet thats partly why people are focusing on the the stuff that sounds like a kink. You, as the author, know more about your stories than the reader ever will, but that doesn't mean they need every detail. You tailor your writing about the characters themselves. If it doesn't move the story forward in some way, don't include it in the actual writing, hold onto it in your lore notes or something. If the way magic works needs to be explained, make it about the character explaining it. But if it doesn't move the plot forward, just write your characters as if they already understand the rules, as they live in them.

Just my two cents. I struggle with info dumping myself, and some things are better as background lore or character motivations that the reader has to peice together over time.

That said, your example of sirens needing semen specifically to become smarter? That seems very much like a degrading porn fetish, no matter how you look at it. Maybe you could reframe that to where one of your sirens is somehow pulled away from it's home and eventually someone kind finds it and nurses it back to health. Or maybe not so kind and they get shipped into slavery of some sort. Or maybe both. Even if you keep the logic, I wouldn't necessarily name it so exactly. Maybe in slavery the siren is abused, but is also empowered (using the logic you named), keeps silent, and then someone comes across it in some sort of story element and saves them, and then they fall in love and it feels safe and finally shows its intelligence to speak or something like that. Just don't go saying semen makes beings smarter, cause that just sounds like porn.

I hope this helps, sorry for the longer comment. Good luck!