I also want to address that the Upper City being a scrapped thing seems to be kind of an urban legend, and I've seen certain things attached to it being spread as truth that are completely untrue (most notably, that this is where Karlach would be fixed and that the current game just defaults to her bad ending)
Yes and no. I can’t be bothered to look up the exact quote, but from what I remember it was explained that there was a lengthy epilogue that took place in the Upper City (and I believe that is what Sven was referring to when he was hyping up x amount of endings). However, it was judged to not be effective and the whole thing was scrapped.
But even if my memory is correct and all I have written is true, none of that would impact content of act3.
