After posting on the Asus forums and unable to get any advice, I thought I would try my luck here and see if anyone had heard of this issue!

I am trying to resolve a boot issue with my brothers gaming PC, whereby upon booting the system stops during post, and we get a message which reads "When raid configuration was built, ensure to set SATA configuration to RAID mode". The only way I can get the system to boot to Windows is to go into the bios by pressing F1 and then going to the boot tab and clicking on the SSD where it says Boot Override. Once in Windows the system works fine, but the same cycle occurs upon any restart or system start up. I note that this system has never had a RAID config, it has only ever had a boot SSD, and storage HDD.

Things I have tried:

Clearing the CMOS
Trying numerous different bios versions
Changing the CMOS battery
Trying a different AM4 CPU
Trying a new SSD with other Windows install
Trying 1 stick of ram only, and then ram from another system
Setting the bios settings to what is recommended in the error message

System Specs:

Asus B550-A Gaming motherboard
AMD Ryzen 5800x
16GB Kingston Beast 3200 Ram
Crucial P3 1TB NVMe SSD
Radeon 6700XT GPU
Evga 750W PSU

Pretty much all advice I could find says changing the CMOS battery fixes this, but this has not been the case for me. Hopeful someone has some advice on what to try next!

Thank you!