and i don't see option "m.2 PCIe mode" in option "onboard device configuration"
not yetHello! Same issue here, I don't see any M.2 option in my BIOS. I'm running ROG STRIX X299-XE Gaming motherboard. Did you find a solution to it?
Run CrystalDIskMark sequential reads...
If you see 3200+ MB/sec reads, you 100% most assuredly are in PCI-e 3.0 X4 mode....