Happy ending to my story!
If anyone ever has similar issues with the As Rock x570 Creator.
The G Skill Trident Z Royal 2x 16 GB C16 works but only if you set the voltages manually.
Seems like on Auto the voltages on that board are needlessly aggressive.
Here are mine now.
Load the XMP profile and then manually set the below:
Dram 1.35V
Soc 1.05
VDDG CCD 1
VDDG IOD 1
VDDP 0.950
Like Daveotero above, I too registered to say thank you, Mannymac!
I've had random reboots on my ASRock X570 Phantom Gaming ITX-TB3 board with G-Skill 3600Mhz CL16 RAM and a Ryzen 9 3900x CPU with fabric clock at 1800Mhz. I'd tried everything I could think of with varying degrees of failure, with the best outcome being the odd reboot here and there.
Recently I stumbled on your post while trying to figure out what was going on, then changed my BIOS settings to reflect those given and now the PC seems to be as solid as a rock, with the RAM running at 3600Mhz and a coupled fabric clock at 1800Mhz. It looks like perhaps there's a common theme with ASRock boards that the voltages are aggressive out of the box, causing system instability. Massive thank you for posting the solution, and for restoring my faith in my PC!