Aug 01 10:36:06 localhost kernel: ahci 0000:00:17.0: Found 1 remapped NVMe devices.
Aug 01 10:36:06 localhost kernel: ahci 0000:00:17.0: Switch your BIOS from RAID to AHCI mode to use them.
You’ve correctly guessed the problem: Endless OS 6 is not compatible with this mode.
It was supported in Endless OS 5 and older, but support was removed in Endless OS 6. We made this change because there was no path to this configuration being supported in upstream Linux; it is no longer common in new hardware; and it has become harder for us to support and test. For a specific example, Endless OS 6.1.0 failed to boot on hardware with this configuration, but this was not caught during internal testing or public beta testing, leading to us having to withdraw this release until we could buy second-hand hardware to diagnose and fix the problem.