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 - NotebookCheck.net News
ASRock > B450 Pro4 R2.0
B450m B450 Motherboard Asrock B450m/ac Motherboard Amd Am4 4xddr4 128gb M.2 Sata3 Usb 3.2 Micro Atx For 5000 And 5000 G-series - Motherboards - AliExpress