On B550/X570, the CPU is permitted to provide PCIe 4.0 lanes to the primary M.2 and PCIe x16 slot. On other boards, AMD's microcode limits it to PCIe 3.0.
"A520 isn’t much if any different from A320"
A520 isn't much different from B550. A520 and B550 are both PCIe 3.0 chipsets. PCIe 4.0...