Hello,
I'm a first time user of Unraid, just setting up my first build with a trial license. I have the boot usb drive plugged into a header on the motherboard, I have a USB hard drive plugged into the motherboard externally, and an NVME drive that all show up and I was able to configure them in my array. I also have two drives connected over SATA (one sandisk SSD and one WD Red HDD) that do not show up in Unraid. They do however both. show up in the BIOS.
I searched online, and found suggestions to disable VT-d/IOMMU in the BIOS, which I tried, but that didn't fix the issue.