Thanks for the log, it’s helpful. What I can see in it is that coreboot does not detect that there is a PCI device on your M.2 slot, either the NVMe is damaged and doesn’t respond to anything, or the motherboard/connector itself is damaged and doesn’t connect the nvme correctly to the CPU… or it’s a software issue but since you’re the only one having this problem, and I’ve just re-tested NVMe support on the Librem 15 (with the latest coreboot image, and I tested it with the same 500GB Samsung 960 EVO NVMe), i don’t see how it could be.
The best thing you can try right now is to try the latest coreboot image, and update your machine just to see if it makes any difference. I just announced a build script to let people rebuild coreboot and you can read about it here : Building coreboot from source (official script)
If you have a way of testing another M.2 drive (whether NVMe or not, preferably both) and/or to test that NVMe drive on another machine, it might be helpful.
Good luck.