Graphics card sometimes makes 0% load in the game?

I have a big problem that slowly really annoys me.

Strange white I can't fight in Fortnite because I get huge FPS drops. The Afterburner shows me a big drop of 0% -27% etc. When the GPU is being used, so I'm probably lagging too, right?

I mean, I don't play in high settings either. But more on means and should the graphics work or not?!

With WarZone or GTA I don't have such strange white problems but even there the Afterburner shows me that the graphics card sometimes absolutely gives up the load.

what should I do there?!

I don't have VSync on and my monitor has Freesync (on)

my budget:

ASUS Rog Rx 580 8Gb
Ryzen 7 2700x
Mb B450M Steel Legend
Trident Z royal 3200 MHz dual kit
H115i water cooling.
ST500DM002 hard drive
Corsair Tx 750W

Monitor possibly connected to the mainboard instead of the GPU?

No, the cable is on the graphics card