Editor's take: My days of taking risks with hardware are in the rear view so if it were me, I'd avoid using anything that has been tampered with by a third party. If a Ryzen 5000 CPU was a must, I'd have no choice but to purchase a board that officially supports the platform without any modifications.
When AMD backtracked and formally announced that B450 and X470 motherboards would indeed support CPUs based on the Zen 3 microarchitecture, it was a sigh of relief for those with older boards. Those with even older chipsets like the X370, however, were still out of luck... until now.
Hong Kong news outlet HKEPC Hardware recently received modified firmware for six ASRock X370 motherboards that adds support for AMD's Ryzen 5000 series CPUs. Supported boards include the Fatal1ty X370 Gaming K4, the Fatal1ty X370 Gaming X, the X370 Killer SLI, the X370 Killer SLI/ac, the X370 Taichi and the Fatal1ty X370 Professional Gaming.
It's worth pointing out that these BIOS files weren't officially produced by ASRock but rather, an unknown third party. What's more, while they do add additional functionality to older boards, users still won't have access to PCIe 4.0. Plus, there could very well be some bugs or stability issues that crop up with the use of altered firmware.
Image credit Lutsenko_Oleksandr