AMD Ryzen 5000 Zen 3 support has been added to multiple 500 series motherboards, including the likes of the A520 and X570 chipsets. ASUS, ASRock, Biostar, Gigabyte and MSI are the first manufacturers to add support, but it will be at least January 2021 before 400 series chipsets like the B450 or X470 can run Zen 3 processors.
https://www.notebookcheck.net/AMD-Ryzen-5000-Zen-3-support-is-rolling-out-for-ASUS-ASRock-Biostar-Gigabyte-and-MSI-500-series-motherboards-no-B450-or-X470-support-until-January-2021-at-the-earliest.497827.0.html