How do I have FPS drops despite 3080?

I received the Asus 3080. Everything went well and I had a lot of fun. But when I had to reinstall Geforce Experience because an error code always came when starting, I got permanent FPS drops in Fortnite. I actually always had 240 fps before, now I can no longer play public because they always drop to 6 fps. The graphics card is only used 30% and the CPU about 40%. What could be the reason?

Maybe the disk is busy?

So the last time I had FPSdrops it was in Garry's MOD and it was because my memory was 100%. Since I had to get GMOD with the start options to take a maximum of less ram.