Huge performance issue in fullscreen / 30 FPS lock

So, I'm playing on Steam and performance is very strange. In full screen game locks FPS somewhere about 5-10 no matter the settings. I tried to fix this by simply launching a borderless window, but FPS is still locked, only on 30 now. I have RTX 2060 so I definitely can get 60+ FPS. This is a fresh Windows 10, all drivers installed and up to date, VSync off, XBox background clips (or how this thing called) is off, NVidia battery boost off, so nothing should give such an effect. Any ideas on how to fix it?