I am glad you decided to simplify your system for testing, that should make it easier.
Do you change anything in the Bios so you could run Raid? On one system I have there is a Intel RAID controller you can turn on but I only saw it in simple mode.. It may have been a different motherboard..
It appears you saw the comment about RAID required non-Intel drives be inserted in the two PCH attached slots. But just that still won't let you set up a RAID array? Where do you set up the RAID array, in the Intel Rapid Storage controller? You can probably tell I am not a big fan of RAID..
These boards can be so complicated as to what can go where that it makes it hard to get the correct placements..
Maximus Z890 Hero,
Intel Core Ultra 9 285K