Seems that you dont like to read or skipped important details, read it again (the 2 guides) and do not skip any detail, thats what kills a man…
[HowTo] Get full NVMe support for all Systems with an AMI UEFI BIOS - Special Topics / NVMe Support for old Systems - Win-Raid Forum (level1techs.com)
The error you got its correct, because it seems you didnt pay attention to what i wrote about Asus bios.
*A current backup/dump of the system bios is a MUST for recover methods and risks of fail flash, that can break the system, as is all over the forum written.