PCI-e bifurcation explained
OK, some asked about 'what is bifurcation' from the previous post. Essentially, if you have a PCI-e x8 slot, you can split it in half and make it 2 x4 slots. If you have a x16, you can make it 1 x8 and 2x4, or 4x4.
You can see below, i've overlayed my BIOS setup on top of the motherboard diagram (here a SuperMicro x10DRi-LN4+). Now, if your BIOS doesn't have a bifurc option, you can possibly get it to do so by adding support into the BIOS. I'm not going to help you with this, its very complex, but I was able to add both UEFI NVME boot and bifurcation to a different SuperMicro motherboard by adding the UEFI modules into it manually. YMMV. Void where prohibited.
So in my case, I have a NVME carrier which is capable of holding 4 NVME drives. It is passive (no PCI bridge is onboard). This means that it is conceptually 4 PCI-E x4 drives. Without bifurcation, it just won't work. Some people refer to this as 'pci splitting'. You may see references to this in the 'crypto-mining' industry, where people are using 1x interfaces via cables to mining ASIC.
Be careful here, bifurcation is supported on server motherboards with modern chipsets, but its support on desktops is not as universal. And just because your motherboard supports it doesn't mean your BIOS will.
It may also have downstream affects on other PCI-e cards, e.g. reducing their lane-width. Caveat Emptor.