Video hardware or driver is the most likely.
Yeah, I wouldn't suggest going scorched earth just yet.
That's a good point Jim, I didn't mention updating the Nvidia driver manually.
Windows does usually install an older one (sometimes significantly older) as part of it's setup / hardware detection process.
Tk, on this fresh windows install can you attempt installing the latest Nvidia driver from them?
https://www.nvidia.com/en-us/geforce/drivers/ Do a manual driver search, and get the 'Game Ready' driver. When you install it, you can uncheck GeForce Experience (you really don't need it for much unless you're interested in HW accelerated remote desktop streaming) and make sure to check 'clean install'.
I don't *think* this will fix your issue but it's definitely worth a shot since it's really 5 minutes of your time.
Yeah it could be your RAM or your Processor or your Motherboard (ah the worst thing to diagnose, maybe even worse than memory), but we'll consider it a remote possibility at this time. The GPU is where you should focus your effort at the moment. Do you have access to another 30 series GPU *OR* whats Amazon like in your country? If you can order from them, you can snag a 3060ti, and just return it if this behavior persists.
I haven't had experience with AMD GPUs + MadVR in 10+ years so I dont' have a terrible amount to add on that front. I have a 6500XT that's actually being returned right now because I bought it for 120hz linux desktop stuff (also messing around with Wayland and HDR) and it kind of was a big disappointment, both from both a performance standpoint as well as the drivers. Say what you will about Nvidia and their closed source driver nonsense, their stuff does indeed work quite well.