My dirt cheap Asrock A320m-ITX and my mid-level Gigabyte Aorus Elite x570 support bifurcation, did the feature become much less common in the last couple years?
https://forum.level1techs.com/t/any-lga1700-motherboards-wit...
Some boards will only bifurcate the x16 slots into x8/x8 mode, which is sufficient for an x8 GPU with one SSD attached to the spare lanes, but that still leaves 4 lanes unutilized. Adding two SSDs to fill up the bus requires support for x8/x4/x4 mode, and an x16 carrier for four SSDs requires support for x4/x4/x4/x4 mode.