PC slows down after a while

Specs;
16GB RAM 3200 DDR4
AMD Ryzen 5
NVIDIA 2080
512GB SSD

My PC has been great for ages but recently when I start playing games after about 20 mins it slows down to the point where stuff in unplayable. Doesn't happen when doing other stuff like web browsing, sometimes youtube stutters but that's probably my internet.

Is it worth resetting windows to see if it fixes this?

Happens on any game. I have checked drivers and they are all up to date.