I just jump to say that all I had to do was disable fast boot from BIOS. (It was already in legacy mode, secure boot disabled)
Had something like this with a Dell Latitude 5591 and SK hynix P31 NVMe; solved (or seemingly doesn't happen anyway) by switching to a Samsung NVMe. I re-seated, tried LBA 0 and 1, AHCI and RST, and it was only with that P31 NVMe where it'd sometimes not be visible for boot regardless of OS.