How to enable 4x4 bifurcation in Asrock B450 Gaming ITX/AC?

I need two PCIE SSD and a RAID Controller,
but my board has only one M.2 slot and PCIE slot.
BIOS setup has only 2x8, PLX card is too expensive.
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@efsg - what BIOS version are you using? I checked latest, and I see plenty of different options for this, some sets of which would be some hidden from you for that setting generally, but I don’t see the specific ones you show, so I think you’re not using the BIOS I looked at
Also, you can use 2x8, that will work fine for 4x4 setup

Thank you! Update to the latest version BIOS can use X8+2X4 and 4X4