B450 Pro4 5 beeps no display

yea went back to using i5 9400f and not going to touch amd any time soon

Found part causing issues
after yeeting b450 asrock(am4)
for Z370 gigabyte (lga1151)
PC with CPU not having iGPU posted no issue
so looks like mobo was faulty

I wouldn't mess with downgrading BIOS versions. I also highly doubt it's RAM incompatibility.
The 3600 should support all the same RAM that the older architecture 2200g did.
Manufacturers don't test every single RAM model and brand with each architecture.
Generally, if it's compatible with an older model CPU it will also be compatible
with newer ones.

If you want to go ahead and try more things, before you mess with BIOS downgrades etc
I would suggest trying various BIOS settings with the 2200g installed that have
to do with the GPU and PCIe.
Maybe try and set the PCIe to PCIe 2.0 or 3.0 manually then reinstall the 3600.
Ideally I would have liked to see what happens if you use the other PCIe slot
but you said that isn't an option. I have a suspicion that the system will output
a display if you do.

I am off to bed but I will check back here in the morning.

Good luck

try getting to run this PC with older Bios version like
4.9? which added auto disable?
rn it's on P8.02

I feel like we are missing something obvious here. It may be worth picking up a
display port cable before going down the route of switching to another APU. It
can even be a display port to HDMI cable so long as you hook it up to the DP output
from the GPU.
Silly question but I have to be sure, you do have the HDMI cable connected to the
RX6600 not the motherboard yes?

If you like you can also try opening a support ticket with ASRock Tech Support:
https://tw.asrock.com/events/tsd.asp

They may be able to suggest something I haven't thought of, they know their products
better than I do.

Good luck