Update #3 - Resolved:
It was the Windows USB drivers (both 2004 and 20H2).
After going back to my motherboard's (Asus X79) 2016 drivers, I have a stable system.
Update #2 on disabling CPU C-states:
I got a "semi-freeze" where the task manager will show 0% CPU utilization for every process listed, chrome menus will respond but be invisible (with just an outline), and CTRL-ALT-DEL will allow choosing log-off or shutdown but neither of these actions will
ever finish. Choosing "lock", instead of log-off or "switch user", (the latter does nothing as well) will apparently lock the screen but entering your pin will not unlock anything (screen blank) and after that point, CTRL-ALT-DEL will not show anything either.
I am writing all this in the vain hope that someone from MS, who might have a clue, might read it :)
What I am trying right now, in addition to the disabled C-States below,
is disabling Hyper-Threading - which, from the above symptoms and the OS
microcode updates, may stand a chance of being a/the culprit.
I will update if I get another freeze with both of these disabled (C-States and HT).
Update on disabling the monitor sleep mode:
It fixed the "complete" freeze, but I still got a "partial" one (which shortly thereafter becomes complete, haha - I will explain).
It occurs on the logon prompt: The keyboard will not work. In fact, either of two keyboards will not work. (USB, one wired, one bluetooth, and yes it happens with the bluetooth unplugged). Not even the num lock status will change.
The mice will work and the screen will respond to, e.g., clicking the power icon on the logon prompt and choosing shutdown. Following which, the PC will finally freeze completely (no blue screen).
WhatI am trying right now is disabling all CPU C-States above C1E (which remains enabled, along with EIST) in the BIOS.
Original post:
I have the same freeze issues after upgrading to 2004. Prior to this upgrade I would have weeks of uptime.
I have found that setting the monitor (not just the PC) to never sleep avoids the problem. Note that the screensaver is unrelated - this is the setting:

I enrolled in the beta and moved on to version 20H2 (build 19042.541), in the hope of fixing the problem but I've had it happen in 20H2, too. The only solution is to set the monitor to never sleep.