Then choose other port, otherwise you don't have enough lanes to spare with x16 graphic card installed, unless you manually limit that slots lane width to x8
vROC is only one kind of RAID, there is several other methods, but manual says RAID must be used, and with only two cards installed I've seen several users only see one until they went to setup array.

Advanced >> PCH Storage >> Hyper kit Mode (Enable this)
Advanced >> Onboard devices >> Also notice the two PCIE lane settings here (PCIEX16_2 Slot Bandwidth + PCIEX16_4 Slot Bandwidth)

* Edit - @frogger - I did some testing as I mentioned I would

Z490M-Gaming-X + G5900 Celeron 16 lane CPU, onboard graphics used and Hyper in main PCIE x16 slot
Hyper V2 + 2x Intel SSDPEKKF256G8L (Enterprise 760p)
"RAID" mode not set in BIOS, AHCI is used
Bifurcation set to 8x4x4x or 8x/x8 (only options in this BIOS as it is)

So, it seems RAID is not a must! But, it IS about what slot you use on the card, as well as what bifurcation options are applied to the PCIE slot being used!

NVME in Hyper slot 1+2 from top, only one NVME visible in BIOS/OS >> w/ either 8x4x4x or 8x8x set
NVME in Hyper slot 1+3 from top, both NVME visible in BIOS/OS w/ either 8x8x or 8x/4x/4x
NVME in Hyper slot 1+4 from top, both NVME visible in BIOS and OS ONLY w/ 8x4x4x - with 8x8x set only one NVME visible in BIOS/OS, same as if slot 1+2 is used

If you need me to re-check with non-intel NVME's to confirm they act same, let me know

4x4x4x4x may have different results than my above testing scenarios, or things may also be different with other CPU's w/ more lanes avaiable, I am not sure.
But, seems to me, at least for two NVME, set 4x4x if possible or 8x8x, or 8x4x4x and use slot 1+3 or 1+4. You may need to find which slot 3/4 works best for your second drive, with whatever bifurcation setting works there to make both appear.
Seems 1+3 is best choice, at least that slot worked best for me with two drives and the limited lanes and bifurcation options I tested with.

Also, it's probably best due your limited lanes as well, to find which slot has most available lanes to you, or which has enough for what you need, that also offers 4x4x only, 8x8x, or 8x4x4x etc, so lanes are not wasted.
Ideally, find which slot works with IOU2 from each IIO, because that one offers 4x4x and that is all you need here.

* Edit - Follow up RAID creation testing - I tested, and seems I can only create an array within the BIOS with Intel branded drives, other brands only one shows up so can't create array (no matter the BIOS config)
I did not test in OS. So, VROC Ket may be required to RAID non-Intel drives, I am not sure.

Thanks for that, it helped me understand more about the subject.

I've tried everything I could find and think of and nothing work so I'll just wait and upgrade to a 40lane cpu if I can find an affordable option.

@frogger - You're welcome! Yes, it could be due to CPU limited lanes and how they are laid out on the board. So, no cheap x40 lane Xeon or regular for x99 yet?

need decent single thread performance so I was looking at 5930k or similar. Cheapest I could find on ebay or localy is around 300$ cad for a 6850k. Good thing about 40lane is I could get 2 more drive, but I'm not sure, will think about it.

Wow, yes, that is still high prices for such older CPU's, I can't believe their prices are still this high!!

Checkout Xeon's in Server and main CPU desktop area of ebay, sometimes these are much cheaper than regular CPU