While the m.2 slot of the 3rd generation X1 Carbon is allocated 4x PCIe 2.0 lanes, it only supports AHCI PCIe SSDs for booting. According to some forum posts, it appears this is a BIOS established limitation imposed by Lenovo, and it actually allows for R/W of said drives. One way I've looked at getting it to work is using Coreboot with SeaBIOS, which does support NVMe, however this seems unnecessarily complicated, and has a high rick of bricking the laptop. Later models of X1 Carbon does support NVMe, so I'm just wondering if anyone here would be able to take elements from the newer BIOS to modify the current BIOS, or can tell he how to. Source: manjaro forums: /t/boot-issue-on-lenovo-x1-c3-with-nvme-ssd/36190 Tom's guide forums: /threads/carbon-x1-3rd-gen-nvme-support.397269/