Yeah, that's not really possible. Showing only what an MC sees would lead to a story that makes no sense. To make such a thing work you still kind of have to act on third person omniscient rules, but you have to limit what the player sees. So, they wouldn't see free roams or sex scenes because that's kind of the point of a "True" POV. We'd still see cutscenes in which story important details happen, so the duke and his conspiracy scheming, or them finding the statue lost at the start of the game, or the duke and Rose discussing something story important before they have sex. You still need to tell the player the story you just have to cut the "private" content out. This kind of PoV should make the player suspicious of what the women are up to with their NTR partners without having seen the full details.
So in terms of free roams you no longer show the ones we technically can't see. No more talking to people with hearts over their head to see a flashback, no more walking down a hallway and finding a pair of rogue panties that a maid snatches away to bring back to the duke for a scene with her and Rose, no more walking down the street at the docks to see Cyanna and Ulrod fucking behind a building. Instead we see shaded figures behind curtains, hear moaning and groaning behind closed doors, but do we see the top of Rose's head when she's giving the duke head while he looks out a second story window? No. Do we see Ulrod and Cyanna fucking down a dark alleyway? No, we see their shadowed out figures and hear the moans.
A "true MC PoV" should still tell us the story but limit the sexual content to what we can actually see. This is really the only way to make such a thing work without forcing the MC to be present for a lot of stuff they shouldn't be there for.