I believe Fischer would win 6/10 times. Magnus is definitely the best (statistically proven) player of the modern era, but even as someone who has grown up in the prime generation of Magnus and wasn’t even alive at the time of Bobby, just going back and seeing the Brilliance of some of Fischer’s moves…. They’re undoubtedly next level brilliancies that I doubt even Magnus himself would find. With that being said, unfortunately, with the technology being the way it is today compared to what it was in Fischer’s time, Magnus will most likely always be considered the GOAT since again, statistically based off of the more we know on Carlsen and the lesser we know on Fischer, Carlsen is more proven.