There is no real 18+ Version! They switched from hardcore to softcore mid-development and the product, as it is on steam (Iragon and Iragon 18+) IS the final release. And 18+ means "showing boobs and covered up bodys rubbing on one another" and NOTHING more.
Todays announcement taken from their discord server: "[..] Regarding our last project. As we’ve said before, we’ve read all of your feedback and we know that many of you are unhappy with the direction we decided to take. We chose to avoid hardcore sexual content and instead make a softer erotic game. We’re firm on our decision and will not be making games with hardcore sexual content in the future."