I've been playing a lot of Fortnite on my PC lately. I have a 240 Hz monitor, I'm aware that my PC does not achieve a constant 240 FPS. But I find it strange that I drop to 4 FPS on Full HD and low graphics settings! Got… I would argue that my PC is not bad. I have the latest driver version and even reinstalled Fortnite.
Here are my components:
Kolink Observatory RGB white with glass window
AMD Ryzen 5 3600 (6x 3.6GHz / 4.2GHz Turbo)
be quiet! Dark rock slim
MSI B450-A PRO MAX
16GB (2x8GB) DDR4 GSkill 3000MHz AEGIS
960GB Patriot Burst (560MB / s - 540MB / s)
8GB Powercolor RX 5700XT Red Devil
500W be quiet! PurePower 11
You may need to turn down the FPS in-game. This means that the PC can compete better and it remains more stable. And I find 240FPS strangely high. Heard a maximum of 120 FPS. But also from 60. Allocating more RAM (not in Windows but in the game settings!) Does nothing, at least for Minecraft. If the visibility is at maximum, he poops, or Laggt.
In low settings, the 300+ FOS manages with the same components. There has to be something else.
Try to reinstall the drivers. The AMD cards especially the 5700XT had many driver problems. If this does not help, try an older driver version.
Edit: Funny idea, but could it be that your GPU is underutilized in low settings? What happens when you screw this up? Still dropps?