Alright I finally have tried this on Windows 10, GTX 980 and a 12900k, but the framerate does not go above 35fps, gpu and cpu seemed very fine, so it seems an internal problem but I cannot find what it is since I used the same config that brodostar used in his youtube video. FPS would be same 30-35 with both heavy scene and even with a single GK on screen.
Checking skip access and disabling internet didn't help.