i think they're referring to "futa". it was a legit japanese word that originally meant "androgynous" or "hermaphrodite" but since hentai became more widespread its meant "woman with a penis" and is generally like. a fetish-inspired slur towards intersex/trans people.
Honestly, I'd suggest that you continue doing your own thing and don't listen to what these internet trolls says.
I love the content you release, and best part.. You make it free. Up until you start charging for your content and have to actually worry about pleasing the masses, don't listen to us.
Keep doing what you do. :) Thank you!
Hermaphrodite is the scientific term (usually used for animals) for a species like snails or certain types of geckos and fish that have both ovaries and testes. intersex refers specifically to people who were born with a non-standard set of genitals (ie has a penis but also has breasts, or has a vagina and no breasts) but its often used as a catch-all in porn for anyone with something other than "just a penis and testicles" or "just a vagina and breasts"
it would just be semantics if people hadn't started using them as slurs, but they did :/