Why do my games jerk constantly?

I have a PC with the following features:

CPU: Intel Core i7 9700k

GPU: Asus GTX 1070 8gb

SSD for games: Samsung 970 Evo Plus

RAM: 8GB

What could be the reason that I e.g. Fortnite always only have FPS between 80-130 and now and then briefly stops the game completely? (So short lay for half a second or so)

In the games my CPU is always 90-100% full, so do I have to buy a better CPU cooler? Or is it the RAM? (In Fortnite it is approx. At (80%))

Or is it the mainboard?

Beautiful good day

it shouldn't normally be due to your equipment. Open your task manager and see how Fortnite reacts.

It also often helps to raise the priority