Yeah, game features like fisting mechanics. No game in existence (except if you want to waste three years in VAM?) has dynamic, non-preanimated fisting, that would actually be a valuable mechanic. I don't want gallery scenes, I want gameplay sex. I want to roll for anal circumference lmao. How hard is that to understand. There hasn't been a game since SuperDeepthroat that had good sex gameplay. And instead of doing anything remotely like that, the devs seem to have their sights set on making a SURVIVAL CRAFTING RPG #385653
Hold on, let's rewind. The moment you mention "SuperDeepthroat" as a game for good sex gameplay I understand your frame of reference is super dated, like from over a decade ago during the Macromedia Flash Game era. So hold that thought and answer for yourself the following: when you played SDT, did you have fun A) customizing the girl and boy, B) Playing with the dialogue system to trigger emotion and action changes, or C) modding the game with custom SWF content for diverse shapes and backgrounds?
Regardless of your answer, you're looking for a gallery game. Games like Honey Select 2 and its studio hold your answer. If you want to design characters with mild choices in personality and sex properties, Koikatsu focuses on personality just a touch but it's way more than HS2. If you don't mind a lack of voice acting but want the potential to create weirdly behaving NPCs with nuance, try Artificial Academy 2.
Now that we're past that: Carnal Instinct is like Skyrim but without mods but with the logic of porn mods fitted into the story from the base foundation. In exchange for mod support and sex everywhere you get erotic storytelling from the foundation for a cleaner though dryer experience. This game won't hold much of what you want besides that one island that's all sex all the time. Sorry, with this game you're out of luck.
Try Karryn's Prison though, you'll find plenty of sex everywhere, gameplay is good from the start, and a certain overhaul does more with edicts and progression for yet more gameplay. If you want less game and more sex, try Unaware in the City. And for good combat and literal fisting mechanics, try Pain Re:In.
Maybe I can come back to edit my post with links, but for now please use the forum search function.