Zen 3 processors require AGESA v2 1.0.8.x firmware or higher. I doubt that the board is already delivered with this AGESA version. Since I bought the board more than a year ago, I unfortunately cannot say whether "new" boards are already delivered with the corresponding AGESA version. However, MSI offers the corresponding BIOS for download on their homepage.
Flashing a current BIOS should actually work with a Ryzen 5xxx processor, the board has a "flash button" and a corresponding USB port to flash a BIOS directly from a memory stick. This works as follows:
- Connect your power supply to the board. It only needs the following power connections: CPU_PWR1 and ATX_PWR
- Format a USB memory stick (not larger than 16 GB!) as FAT32, e.g. with diskpart.
- Get the latest BIOS from the MSI homepage.
- Unpack the file, rename the main file (not the .txt file) to MSI.ROM and copy it to the stick.
- Insert the stick into the USB port described in the manual, WITHOUT powering the board.
- Press the button at the back of the board labelled "Flash BIOS". Wait until the flashing LED by the button stops flashing.
- Your board now has the latest BIOS and should POST without any problems.