If there is no BIOS update from the motherboard manufacturer (or even if there is, the Phenom is an old CPU), simply take ownership of the mcupdate_AuthenticAMD.dll in C:\Windows\System32 and rename or delete.
Be aware that future updates, upgrades or sfc /scannow will replace the missing .dll and revert your system to it's current state.
AMD Ryzen 5 5600X, Corsair 32GB DDR4-3200, Gigabyte B550 GamingX v2, ASUS TUF Gaming RX6800 16GB, Corsair RM750i, 2TB Samsung 970Evo Plus NVMe PCIe x3, 512GB Corsair MP600 Force NVMe PCIe x4, 2TB Seagate Barracuda SATA-III, ASUS BW-16D1HT BD-ROM Writer