Which Slot to use?

2 specification supports NVM Express as the logical device interface for PCI Express SSDs, in addition to supporting legacy Advanced Host Controller

ON your board, the slots support both SATA & NVME but not at all speeds this means top slot likely supports PCIe 4 and bottom supports PCIe

nvme m2 slot laptop 2 SSDs with B+M keying maximize compatibility in both slots, and will operate with 2x lanes of bandwidth SSD keying SSD Length As the

nvme vs m2 slot difference Find out which SSDs can be used to expand your PlayStation®5 console storage space, and how to insert an SSD into the expansion slot