Can I do x8/x8 with BIOS modding?

[inf3rno]

It is very hard to find a consumer grade AM4 uATX board with two x16 slots that supports dual x8 mode. Actually I haven't found any, there are only ATX boards with this feature as far as I can tell. The Ryzen CPU supports it, and the motherboard does not have to do much to make this work as far as I understand. So is it possible to enable x8/x8 for the two x16 slots by modding the BIOS, or is there something here that I am missing?

Just a small example: ASRock Fatal1ty B450 Gaming-ITX/ac supports x8/x8 on a single slot with a bifurcation riser card, while ASRock B450M Pro4 does not supprt x8/x8 on two slots. Same vendor, same motherboard chipset, same CPU...

(note: Your page totally falls apart in Firefox, I had to use the developer tools to be able to send this question.)

[inf3rno]

I checked meanwhile, dual X8/X8 is not possible because the motherboard is not wired properly for it and somebody said it would need multiplexer too. On the other hand single X8/X8 is possible on the first slot if it runs in X16 mode. So in theory even the firmware of the very cheap uATX motherboards can be modded to support riser cards, which would be around half price compared to mini-ITX boards with riser card support. Here is a description: https://hardforum.com/threads/pcie-bifur...1043385990