You may want to disable the Quiet Boot option in BIOS under the Main tab. With the onboard controller you should be able to get a CTRL+E prompt to enter the RAID BIOS.
I noticed that the second drive is a 4TB drive. The onboard solution is not offering support for drives larger than 2TB. You might want to remove this drive and compare results. In any case, remove them both and see if you can see the RAID BIOS prompt.
You cannot enter the RAID BIOS if no drives are detected but at least we can see if the controller is attempting to initialize or not.