Lets start with the most important...
What are your hardware specifications?
What have you tried so far?
Windows 10
Motherboard: MSI MPG Z390 Gaming Edge AC
CPU: I7-8700K at 4.8Ghz
RAM: Kingston Fury 16GB at 3200Mhz DDR4
Graphic card: Rtx 2080 ventus 8GB it's overclocked
And the game is running from an SSD at a resolution of 2560x1440
I've probably tried about everything, bnsbuddy, changing graphics settings, removing shaadows improves a bit but at my specs i would espect to be able to play with some detailed graphics.
I've tried nvidia control panel adjustments, task manager adjustments as affinity , priority..
At some zones the fps are ok at 70-80 but very unstable , fps fluctuating a lot , and as low as 30-40 in some more dense zones, it's funny because even with the option that puts all to minimum for low end pc the game runs exactly the same.
If i put the game at ultra the performance is terrible until i disable shadows , but even then i would expect to able to play smoothly