Cross-flashing retail BIOS to HP Prebuilt

I recently picked up an old HP 285 G3 Tower PC from an auction site that I’ve been playing around with, specs as follows:

AMD Ryzen 3 2200G
8GB DDR4 RAM
256GB NVMe SSD

It has a proprietary HP AM4 motherboard with an AMD B350 chipset. Now, according to AMD, this chipset can support up to Ryzen 5000 series CPUs, but only with a compatible BIOS. HP never bothered to release a BIOS for this board with the ComboAM4 Agesa to support the newer CPUs, so it’s stuck with 2nd Gen Zen+ Ryzens as the newest CPUs officially supported.

It would be nice if I could put at least a Ryzen 5 3600 in there, so I had a crazy idea: Most B350 retail boards have BIOS updates that support the newer Ryzens, what if I took one of those from a similar B350 board and flashed it to the HP board?

I have a CH341A programmer, so it’s not a problem to flash an unsupported bios and recover from a backup if it doesn’t work.

I chose this board from Gigabyte as the most similar B350 board I could find GA-A320M-S2H V2 (rev. 1.x) Key Features | Motherboard - GIGABYTE Global

My rationale for this being:

-Both boards have 2 RAM slots
-Similar rear IO
-Similar PCIe / NVMe slot arrangement
-Both use SuperIO chips from ITE (though not the same model)
-Both use an AMI UEFI BIOS with a 16MB ROM

Realizing I had a low chance of success, I flashed it and powered on the PC. I could’t get any display output with a monitor connected to the analog VGA port on the integrated graphics, but I got a single “beep” from the board and the HDD activity light was blinking. So I put in a PCIe graphics card and tried again, and sure enough the PC booted into Windows 10 from the SSD.

USB keyboard & mouse seems to be working correctly, the date and time was correct, and I was able to get into the Gigabyte BIOS setup. The only issue is, the PC restarts itself every 30 seconds or so, so I haven’t been able to check much else.

I realize this is a shot in the dark, but does anyone have any ideas how I can fix the restarting issue? All the fans are spinning normally, so I don’t think it’s overheating.