As I recall, there is no configuration menu in system BIOS for bifurcation, only the PCIe gen and link speed.  I doubt that the settings was the issue because you could see the drives in Windows.  Try Live CD or unformatted (unallocated) drives. If you read some similar posts, you will see the common mistake was the issue, not the hardware problem.  Go over your setup, sometimes we can overlook the very basic things in the process.
The subject line says it all: what settings are needed to use the dell quad with more than one nvme ssd? Thanks!
setting bifurcation properly for a dell quad ultraspeed nvme adapter in a T7910