It requires a platform (PCIe controller) and UEFI/BIOS that properly implements PCIe bifurcation (The ability to split-up and re-allocate PCIe lanes electrically). This is mostly limited to workstation and server-tier boards. There are few power-user, enthusiast-tier boards that do it as well.
Gigabyte X670 AORUS-ELITE AX, Raphael 7950X, 2x16GiB of G.Skill TRIDENT DDR5-5600, Sapphire RX 6900XT, Seasonic GX-850 and Fractal Define 7 (W)
Ivy Bridge 3570K, 2x4GiB of G.Skill RIPSAW DDR3-1600, Gigabyte Z77X-UD3H, Corsair CX-750M V2, and PC-7B