Internet bandwidth has no impact on frame rate. If Fortnite is running good enough for you on this machine, great. I would not be fine with playing on minimal settings and with a frame rate less than 60, but your mileage may vary. But finally, a screen capture on top of it will not work. You can try, of course, but I predict failure. The best you can get is probably a jumpy slide show.
Really, don't expect too much. This is or was about the cheapest laptop you can get, worth about $200. There are people struggling at creating good streams on hardware literally 10 times more expensive and literally 10 times more powerful.
I just trying to prevent you from wasting your time on an impossible task.