That's a bummer. My ASRock B450 Fatal1ty Gaming ITX/AC runs a 5700G no problem in an NR200 with 2 case fans.
Cheapest fix is to mod a fan with zip ties or something, to blow right on them. I'd love to read the explanation as to why the Zen 3 IMC is overheating the VRMS too. It isn't like you threw a higher wattage CPU in there like a 5900X.
The ASRock HDV series, regardless of AMD or Intel, is the bottom of the barrel of the line up every gen. I put this issue squarely on the board, not the platform. Having run almost every gen APU and every iteration of AM4 CPU on an ASRock Fatal1ty X370 Gaming X. I also ran a 3600 with 3200MT/s in a $50 MSI A320 and couldn't tell the difference in performance between it and a AORUS ELITE B450 at the time.
-Just picked up a pack of 60 small VRM heat sinks + Thermal Adhesive for $10 off Amazon. Apparently reasonably popular among the GPU water-cooling crowd to ensure their GPU VRMs don't fry without the stock cooler on them.
Will paste those puppies on to the MOBO VRMs and see if I can reign in temps and bring about solid stability (at any RAM speed).
What I do find interesting is in this new BIOS if I enabled XMP (which bumps RAM voltage up to 1.35v) on my 2200g there were no issues but with the 5600x the voltage is highlighted red for some reason, like the board is telling me "this is gonna be a problem yo".
What's really rustling my jimmies at this point is the system isn't "passing" p95. Runs it for a while then hard resets. I know virtually no gaming workload is ever going to stress a PC like a P95 torture test but just the knowledge that the thing isn't absolutely rock solid is kinda pissing me off.
That said wife has played an hour long sesh of Hogwarts (running a solid 60FPS high now with FSR as opposed to dropping into the 30's like it did with the 2200g) as well as Portal 2 for an hour at like 300FPS without any instability or crashing. 3dMark is stable as well.
I'll keep monkeying with it for a while and seeing if I can achieve that elusive p95 stability, but the goal here was to make a spare PC out of parts I had lying around with one relatively cheap but substantial performance enhancing upgrade, but now I'm finding myself back on ebay shopping B550m boards and crap. Wife says I'm being a moody bunghole too, so I need to just put this out of my mind after a few cheap fix-it attempts.