Insta-Dice simply uses the non-physics based rolling mechanism already built into FG. So whatever FG uses is what Insta-Dice uses. I'm willing to guess the pseudo-rand on Windows 11 is better than Windows 10.
Insta-Dice, at launch, sets the seed once and does 4 or 5 math.random() (simply for giggles). I doubt that makes any difference, although it is a more recent addition.
Jason