Pc jerks after a while while playing, despite good hardware?

Moin, I just bought a new computer.

My problem is that when I play Fortnite, for example, it runs very smoothly at the beginning and after 5 minutes I get more and more noticeable frame breaks and it starts to jerk, but as soon as I'm back in the menu everything goes well and the first few 5 minutes of the new game go again until the problem occurs again…

My specs are:

Asus B450

https://www.mindfactory.de/...22726.html

ryzen 5 3600

500 watt 80 plus gold

https://www.mindfactory.de/...11126.html

standard intel cpu cooler

1tb hdd

rtx 2070 great

The game is on the ssd

All drivers are up-to-date, and I've already dragged fortnite over to the hdd and it's just like before…

I'm slowly getting to the end, I've already watched umpteen videos and none of them had the solution.

Do you have thermal paste on the cpu and how warm does it get?

Try to set a fps upper limit (in the game settings) also I would put the priority on performance in the nvidia settings everywhere