Pretty thorough so far. That's good!
My opinion....for what it's worth....
It's not WIndows, or the CPU if it's not throttling. My primary suspects are:
--The keyboard, since it is a known trigger for your issue. Try a basic no-frills cable-connected keyboard
--Audio codec or audio hardware. Have you tried using the Nvidia audio instead of the Realtek?
--PSU. If the PSU is borderline, it can cause all sorts of odd issues with multiple components. Your setup (and OC), needs a quality PSU of more than 650 watts. Ideally, you'd want 15-20 percent more wattage than the minimum to allow some headroom.
-CPU can easily pull over 250W. Does your board have 2 power-connectors for the CPU? If so, use them both!
-Video card up to 120W for 1660ti series cards. Run the "Power" test in OCCT. It loads the GPU and CPU at the same time. It's similar to an intense gaming load, and can help find borderline/faulty power supply.
- Motherboard pulls around 80-90w when overclocked. Make sure the VRM's are not overheating
- 32GB of OC'ed RAM can pull up to 30w. Good airflow over OC'ed RAM is needed. (likely not an issue though)
Lastly, have you tested each RAM module independently? If not, now's the time.
M