Yesterday AMD announced its entry-level A520 desktop chipset for 3rd generation Ryzen processors and possibly for Athlon and Ryzen 4000G processors. Just like B550 the A520 chipset will lack support for AMD’s Ryzen 5 3200G and Ryzen 3 3200G as well as first and second generation Ryzen processors. The A520 chipset will effectively be replacing the A320 chipset, and is very similar to the B550 chipset. Of course the big difference is that it lacks PCI-Express 4.0 completely.
So even A520 motherboards running a Ryzen 3000 processor will not have PCI-Express 4.0 support. The PCI-Express x16 and M.2 NVMe slots are wired to the AM4 SoC are limited to PCI-Express 3.0. Compared to B550 these slots can run at Gen 4 speeds if you install a Ryzen 3000 series processor. Like B550 though the general purpose (downstream) PCIe lanes from the chipset run at Gen 3 speeds, but with A520 you are limited to just 6 lanes.
With A520 you also get up to five 10 Gbps USB 3.2 ports (2 from the AM4 SoC), two 5 Gbps USB 3.1 ports, four SATA 6GB/s ports (ACHI-only), and six USB 2.0 ports.