So the screen turns black but the PC doesn't "restart" or "shut down" until you manually turned it off.
Is this only happening when you are gaming/using high CPU/GPU usages? It could be something with the GPU or the RAM. I have the same motherboard and sometimes, when I turn the PC on, it will do the same-- no lights on keyboard/mouse/headphones but case fans/GPU fans are spinning. I found out it was a RAM issue and set the timings manually in the BIOS by calculating them on Ryzen DRAM calculator and everything has been working fine. I also had my PC restart several times during gaming and found out in Windows Event Viewer that the reaction was Kernel Power 41. So, I replaced my PSU (that wasn't the fix) and ran a corrupt file scan through Command Prompt (Admin) and that fixed my PC restarts.
This is coming from my experience but it could differ from you.. RAM is not always "Plug and Play" and so manually changing the timings and the speed is better than using XMP.
With the white screen and all of that, well I'm not too sure.. It may sound like a problem with the GPU but I'm no expert. Are you on the latest drivers? If you had an NVIDIA GPU before, did you uninstall those drivers using DDU? The old NVIDIA drivers could be interfering with your AMD ones if you had that installed before. If not, then don't worry.
Try clearing the CMOS and see if you get any crashes while gaming at 2133 MHz. A failed post could be the RAM so I would clear the CMOS by taking the battery out for a minute. This will set your ram speed back to 2133.
Is it possible to test the GPU in another system? Maybe run some memory test to find errors?
Sorry if some things I say don't make sense.. I'm a new builder as well and I'm learning everyday.. If anyone else sees a statement I have said that could be incorrect, please tell me