Look, there are plenty — literally hundreds — of games on F95 where a harem is possible (or even planned). Retrieving the Past isn't a game for you if harem is what you're wanting. That doesn't make this latest season some kind of bait-and-switch as implied. It just means you misunderstood the point of the story. The basic plot has been, all along, that there is some secret government program that has at least partially gotten out of hand. (And, ofc, more details and plot points have been introduced as things have progressed.)
It's been incredibly clear since at least Series/Season 2 that a harem isn't going to happen. Nearly all the women from S1 stopped going after the MC's cock and moved on with things. For instance, while Mei still loves the MC, she's not in love with him anymore. The Nicky-Vicky branch has been made clearly since even S1; they would force you to make a choice. (Hell, the MC himself says he'll need to choose.) Amber is actually his daughter, and when you see the choice for Nicky (pursue romantically or not) it's clear that the MC isn't OK with incest; so that rules Amber out.
If you had the impression that there might be a harem and this were still S1, I could understand, but any illusions of that should have been lost by playing through S2. I understand that you are disappointed, but the good news is that there are loads of harem games. If you haven't already played them, you might consider Midlife Crisis, Parental Love, Polarity, Soul of the Paintings, WVM, Bad Bobby Saga, Bad Company, Lust Epidemic, Harem Hotel, or Harem Resort — just to name a few off the top of my head. All of those either have strongly established paths for a harem or are specifically set up for the MC to build a harem.