> Our network cards need PCIe 3.0, so that disqualifies 5 chipsets right away: only the A520, B550 and X570 chipsets remain.
No, the linked Wikipedia page only shows the PCIe lanes connected through the chipset and doesn't account for PCIe lanes provided directly from supported CPUs. X470 supports CPUs which have PCIe 3.0 and a board with x8/x8 mode like the ROG Strix X470-F https://www.asus.com/microsite/motherboard/AMD-X470/ should work just fine (and has no fan).