Graphic Card capping itself at 30% for no reason

I have Processeur an i7-11800H @ 2.30GHz that runs at 3,5Ghz while gaming, a 8Go VRAM GTX3070 and 32GB of RAM.

Never had a single problem on any game for the last 2 years but recently I've been having a massive issue while playing some games : my GPU just stop doing its job.

Playing Helldivers, I have constant 80 fps for an hour then suddenly it drops to 20 and never goes back up. CPU usage is capped at 33% and won't budge, no matter what I do. CPU is at 40%, RAM at 45%, nothing moves. All my drivers are updated, NVIDIA control panel is set to performance, battery is set to performance mode.

The problem seem to only appear on Steam since FFXIV runs at constant 90 fps and LoL at constant 144 fps.

Does someone have any idea what could be the cause?