@laiviet2811
Typically the graphics card always populates the first PCIe x16 slot for maximum throughput; which is also the default setting; unless you are using the graphics portion of your CPU. Of course not the case here when you have an NVidia 1080Ti…
NVMe typically only needs PCIe x4 slot to work correctly but in your case it is only PCIe 2.0 which is a limitation of the board.
Glad you sorted it all out
Cheers