NVMe expansion card
NVMe expansion card
BIOS should let you set your PCIe slots to x16 or disable them, or choose x8 and x8. You might need to navigate through the settings in the BIOS menu.
It seems the PCIE Raid feature is only offered for the X16_1 and X16_2 slots, not the X16_3. This appears to be an unsuccessful attempt.