.40 file extension for bios update?

Ritzerk, absolutely DO NOT rename any BIOS files!  I suspect that file is a Instant Flash file.  Please look more carefully at the BIOS DL page.  I also suggest you do not update your BIOS unless you feel you know exactly what you are doing.
What are you using to measure the CPU voltages?  Several of the applications give bad results.  I do not know anything about Ryzen Master, but suggest you get CPU-Z.  Hopefully others will comment soon on what is best.  Good luck and enjoy, John.

So you have never seen the CPU VCore voltage and core speeds change depending upon the load on the processor? A dynamic VCore caused by CPU power saving options, a non-fixed voltage mode option selected in the UEFI/BIOS, and the affect of the Windows Power Plan? AMD and Intel have had these features available in their processors for about ten years now, and they have evolved over the years. Turbo boost will cause one or more cores to be at a higher speed than the stock/base frequency specification of the CPU.

That is completely normal and to be expected when CPU power saving options are enabled, and the processor voltage is not set to a fixed value in Fixed mode. Windows is doing various things at random times, so the load on the processor changes. The load also changes depending upon what programs you are running. As the CPU load increases, the processor needs more voltage to run at higher speeds and with more cores running various tasks. You are simply seeing dynamic VCore voltage, that changes on demand, and a dynamic processor core frequency. The CPU temperature also changes with the load and type of load, regardless of the CPU cooler. That is really CPU 101 material.

What system or PC did you use in the past that always used a constant VCore and the processor never changed its speed? You can configure this PC that way if it makes you feel better, but it will run warmer and use more power while it is idle.

Your maximum processor voltage is high because you are using the stock/Auto values for VCore, etc, in the UEFI/BIOS. Every processor is different, even within the same model, regarding how much voltage it needs to operate without problems. A mother board manufacture cannot predict what minimum VCore voltage will be sufficient to prevent a processor related BSOD, etc, so they are forced to set the Auto(matic) VCore value higher than it needs to be for many processors. Note that I said it is higher than necessary for many processors, not that it is too high or dangerously high. As a PC builder, it is our responsibility to set the VCore to a value that works and we are comfortable with.

I see you are using an older version of HWMonitor, or at least one that is not up to date for Ryzen systems. We've seen that with other programs too. Did you really believe your VCore was 2.9V? The most common errors in "calculating" a VCore reading (which is not a simple voltage reading provided by the board's sensor chip, it must be processed from data into a final value) is to be off by a factor of two, or 1/2.

First, you really need to calm down, if you really are scared about what you see in Ryzen Master, for example. You said you don't have any understanding of the UEFI/BIOS option settings, but know enough to change the VCore to 1.375V? Do you still not understand why the CPU speed and VCore are changing?

In your first post you said you wanted the highest voltage to be 1.375V, and did not want it at that value all the time. But it scares you when the VCore is 0.8V or 0.544V?

Now I am confused.