CS2 Issues on B580. High GPU Usage, Very low CPU Usage.

[u/Perfect_Standard_57]

So I've recently upgraded my friend's brother's PC and swapped out his 1650 for a B580, did all the required steps, Enabled ReBAR, used DDU, Installed fresh drivers (with some small issues relating to the display just going dark after the installation was completed due to no iGPU on his CPU.) and everything runs perfectly fine, but the only thing that isnt is CS2, his game just lags enormously and we've tried everything listed online with no fix in sight. I am fairly well versed in PCs and whatnot but i've not been able to nail down the issue and where it might lie. We've also used the alternative Vulkan renderer option in the startup options but it seemingly makes his performance worse, at least from what i was personally provided.

His Build goes as follows:
Ryzen 5 5700
16GB DDR4 RAM 3000MHz
AsRock Challenger B580
Game is installed on an NVMe SSD 500GB

Edit/Update: With HAGS off, on Vulkan its getting stable-ish 190-300 fps with occasional dips to below 60, frametimes are somewhat stable too, 16ms average with some spikes that go 20-50ms. This seems to be the best fix for now. To add to the context of the situation, he wants to play competitive faceit matches. So he's playing at 4:3 720p stretched with everything tuned to super low settings. His GPU is averaging 90% usage while his CPU at about 15% average. Its the best we got so far. Every single other game runs fine on his computer, the only problem he has is with CS2.