Your MSI B550 supports the Ryzen 5 3600 without issues.
Your MSI B550 supports the Ryzen 5 3600 without issues.
In short, you likely need a BIOS update for your MSI B550 to run the Ryzen 5 5600X. The debug light suggests compatibility issues. You’ve already tried flashing via USB, which didn’t work. Choosing a third-gen CPU like the Ryzen 5 3600 seems safer since it’s confirmed to work without updates. Your concern about the BIOS is valid—making sure it’s compatible is key.
All B550 models come pre-installed with support for Ryzen 3000 series (non-G) components. A functional Ryzen 5 3600 would require no BIOS upgrade to start up on a properly configured B550 board.
You're likely to get no issues with your new B550 board and Zen 2 chipset. MSI probably has some guides on using the flash button—check them out if you haven't already. Do you have any spare DDR4 RAM left? It might be worth a shot. Please share an image of the internal components if you're unsure.