Generally, it seems to fall into a few categories:
Narration and/or images, maybe with a few binary choices
Animated scenes with some form of interactivity, like setting tempo
A set of actions you can choose to perform, which fill a lust meter or similar (sometimes you also spend stamina points, and it can be based on your game stats)
Which do you prefer? Does it depend on the game genre? Are there any presentation styles that don't fit into the above?
i've generally concluded that, if a game is gonna have sex, i want it to be explicit about it (e.g. hentai games vs bioware games); for example in baldur's gate 3 it always feels a little weird because it's more about intimacy so it's always followed by a cut to black before the action happens
a lot of hentai games straddle a weird line of their own though, because they often have their most titillating scenes around gameplay (so you're focused on gameplay and not titillation); it's preferable to have the sexy parts separate from gameplay, but that has its own weird disconnect
the only game i felt like did this well is orc massage (you can find it on steam); it has gameplay but no time pressure; it also rolls foreplay into it (because you're an orc... massaging various sexy girls); it does a nice job of allowing you to get plenty aroused before you see the action and can get to action yourself (which is a sort of usual thrusting / set the tempo / cum when you hit the button kind of a deal)
i don't know if you can generalize a genre from it, but i hope more devs try to