did you also flash a new MoBo Bios?
i did so my GA-AX370-Gaming 5 supports Ryzen 3000 - but now i only get 3400CL14 stable instead of 3533CL14!
PC: R7 2700X @PBO + RX 580 4G (1500MHz/2000MHz CL16) + 32G DDR4-3200CL14 + 144hz 1ms FS P + 75hz 1ms FS
Laptop: R5 2500U @30W + RX 560X (1400MHz/1500MHz) + 16G DDR4-2400CL16 + 120Hz 3ms FS