Fps Boost lowers the resolution in some games isn't it?
not in this one. it's mostly in dynamic res games that will run in Xbox One settings instead of One X settings because the dynamic resolution basically breaks when using FPS boost.
we can see this on Series S, which has no choice but play the One S versions, so in games like Titanfall 2 where One S mode also has a dynamic res, the Series S will drop some frames but the resolution will never drop, because it's programmed to only drop if the framerate goes below 60fps... which in a 120fps mode it of course basically never does... so the resolution will also not scale.
this is why Titanfall 2 for example runs in one S mode when using FPS boost on Series X, because on One X the highest res is 6K in TF2, meaning it would only drop below 6k if the game goes below 60fps. this would make the 120fps mode pretty much unusable because it would not be able to run at 6k120fps at all.