This post is old, but hopefully someone else benefits.
[br]
In order to use RAID in this setup, one of the drives HAS to be an INTEL NVMe SSD! That is the only way the RAID will work.[br]
And if you try cloning the RAID to another drive and installing - won't work.
I ended up ditching the 2x 512GB Samsung NVMe sticks and replaced them with 2x Sabrent 4TB NVMe sticks - no RAID, cause it didn't work anyhow!
[br]
Asus tech support is pretty lame in this regards. They knew nothing about nothing and kept reading from the User Guide, almost verbatim![br]
[br]
YMMV, cheers,
MadDogDean