Thank you 
I’m glad I got this working so far and will look into the BIOS mod more closely as RU shows it’s not a board limitation and proof of concept.
I’m using this card: Pcie 4.0 X16 to M.2 M-key NVMEx4SSD RAID Expansion Card Adapter 4 x 32Gbps | eBay with 4x Samsung PCIe 4.0 (running at 3.0 of course on X99) 512GB NVME drives
How can I change the BIOS to make pciex16 work in x4x4x4x4 mode?
Hi folks!
I finally get this thing to work!
With this bios:
As it turns out the BIOS was good from the start.
Bifurcation was working by default.
The reason it wouldn’t work for me was because I had an M.2 card in the M.2 slot all along.
When I was browsing the motherboard description I noticed that even with a 40 lane cpu the PCI-E 3 slot can’t work in 16x mode. (If the onboard m.2 slot is occupied)
So I removed the ssd from the motherboard M.2 slot and put it into the HYPER V2 card, put the Hyper V2 card to the PCI-E slot and voila!
The system saw all 4 M.2 SSDs at once!
And the resizable bar still work as it should.
So, important notification for those who want to use this bios with 4x M.2 pci-e card:
The bifurcation only work in the PCI-E 3 slot, and with empty onboard M.2 slot.
And no further bios settings needed.
Thank you for the support all of you guys!
I have Asus X99 Deluxe II, 6950x, Asus Hyper M.2 x16 card with 4 different ssd (one system bootable)
Thanks so much everyone for the information here!
@superyin really appreciate your guide to modding the BIOS. The copy of the BIOS you uploaded back in 2023 is no longer available from the link. Can you reupload that please?
If anyone else has a copy of the modded BIOS that would be great too, for the ASROCK Rack D1541 board. Thank you!!