Ooh, I tried the red button again and this time it worked, but only on the outer third of it, I think the fact that the menu isn't dynamically refitted to the resolution makes the button hitboxes and their graphics not match. It's not a problem in the middle of the screen where it only seems to make the buttons' hitboxes slightly bigger in both directions, but seems to get worse the further you are to the sides of the screen.
And while this screen looks correct, a few other screens in this game as well as others can have the UI slightly off center to the right which occasionally results in text being cut off.
Since you asked I also tried going into windowed mode and lo and behold, that actually fixed it. I've seen plenty of games where the windowed mode retains the aspect ratio.