So you've ruled out software and third party utilities with a clean install so now we're talking either a hardware or BIOS issue.
- I'd be tempted to disable XMP and test the system for stutters at 2133MHz RAM speeds
- I'd also be tempted to update to the latest Prime B550 firmware as the GPU is newer than your board. Black screen glitch shouldn't happen as the Powercolor card should work fine with the windows default display adpater drivers and anything downloaded from Windows Update after that.
- Unplug anything that isn't 100% necessary to test to make sure it's not some weird perhipheral problem giving you grief. USB headphones, USB hubs, drives, gamepads etc.
If you still have issues with it after that then it's likely a hardware fault. The stock cooler may throttle but it shouldn't cause the issues you're seeing even if it throttles. The PSU would result in crashes, lockups, restarts - not intermittent pauses and stuttering. Either way, you've gone beyond due diligence at that point and should just return it for a refund.
Just read back through this thread, looks like
@Czaxi has already covered the first two, so if it's not a connected device causing the stuttering you probably should take it back to Microcenter and try another one.
I've had several Asus Prime B550 boards running Zen3 without issues. Can't speak for the 6700XT as I'm bulk-buying 3060s at the moment but if this was a widespread problem with 6700XTs it would be far more prevalent on Reddit and other forums for sure.