Poor performance in all games with high-end PC

I use Manjaro but since you have a NVIDIA GPU not sure how well that will work out.. maybe try Pop OS?

Well I'll be damned, I booted a live usb of manjaro with propietary drivers and here is what I got:
https://imgur.com/a/XsGXm5z
Performance all across is basically what I expected from my system +- few fps but that's not an issue right now.
What does this reveal? Is there an issue with windows?
I'm running Windows 10 Pro version 20H2, AMD chipset software 2.05.04.352 (latest)

Try Lubuntu
https://lubuntu.me/
Is possible create an USB live that boot without install on disk, but the video driver not has Vulkan.
If your GPU has Vulkan support need install OS in disk and after install drivers.

If you is using windows install Process Lasso Pro and enable Performance mode.
In BIOS disable all overclocking settings, CPU core boost features and C6-States.
If even after disable continue the same peformance re-enable the options above less overclocking.

re: Lubuntu - There's a reason why I recommended Pop OS, because it's geared towards gaming and getting NVIDIA's driver mess to work properly, no need to invent with distros made for other purposes.
If Manjaro works out of the box with NVIDIA for you, I'd not recommend any Ubuntu based distro over it.

I have no idea what's wrong with your Windows setup then, just wanted to confirm whether it worked fine on different conditions

(You can also get better performance on Linux through further tweaks and game settings)

SPUName with unicode symbols is normal.

If what I suggested so far doesn't work I have no other ideas.
Try live booting a Linux distro and testing it there to see what happens.

What would be the best distro to try?

If I may suggest ...
* How is the use of the Processor during the game? Low use or High use?

* If you use Windows 10, it usually keeps the core active so that Windows starts up faster, but this generates strange behavior after a few days, you can check the time in the Task Manager (CTRL + SHIFT + ESC) performance tab , CPU resource. If you have more than 5 days, RESTART the computer (it's not turning off and on, it's restarting).

* Does the emulator only perform poorly? Videos? Others games or Emulators?

* Are the drivers up to date?

* At Bios does the processor have an Overclock configuration or other customizations? Example CPU calibration

* Are you playing in full screen or window mode? 2 screens? What is the screen resolution and the resolution configured on the emulator?

* Did you try to temporarily disable the antivirus / sandbox?

* Its a 16C/32T CPU so core usage is hard to gauge, but here are some screenshots: https://imgur.com/a/WCT3jCm It seems that at least 5 threads do go up to 100% utilization, I don't know what the ideal should be.

* You can see on the screenshots the up time is low, I always make sure to fully shutdown every reboot.

* Everything else performs within spec of this PC, I linked to a recent Time Spy run with a decent score, all scores are within +-500pts from that.

* All drivers up to date

* All-core OC of 4500GHz with, using Asus Dark Hero with Dynamic OC switch which allows for PBO to still be enabled. This is moot however as I tested this with all values on optimized defaults (i.e. no OC or even PBO), as well as just PBO enabled and the results are all the same. Other applications (Time Spy, cinebench R20/R23, various game benchmarks) DO show the difference when switching from these various OC methods.

* Tried both full screen and windowed, same result. I do have 3 displays running at once, all 1920x1080. Emulator res is default 1280x720 with no scaling (see previous screenshots)

* I had NOT tried that, but I immediately did so after your suggestion. I did notice that in CPU-Z I could now see "AMD-V" instruction set listed under "Instructions" whereas with virtual machine platform/Sandbox enabled I could not see it. Sadly this had no effect whatsoever as you can see on the screenshots.

Quick update, I tried swapping CPU for an AMD 3800XT which is compatible with my motherboard. All other specs remain the same. I observed the EXACT same performance. Of course all other benchmarks did show the difference between CPUs (i.e. scaled lower scores across the board). I searched for rpcs3 benchmarks with this CPU or contemporary ones (not many available) and even those show significantly better performance. Now I have two distinct CPUs both show lower performance from what it is expected in this one application, so I am thinking the issue is another component. RAM? GPU? Are there reported issues with newer GPU architectures? using PCIe 3.0 vs 4.0? There has to be something else that rpcs3 does which other applications dont. As Ani suggested I will try live-booting to linux and test from there. Again thank you for all your help, and if you have any more leads I would really appreciate if you shared them.

* Linux's suggestion is very good for isolating issues from your Hardware. Based on this result, you will be able to focus better on the analysis of Hardware or Software.

- It is a little strange that your CPU has low consumption. With an 8 Threads processor and 4.0 ~ 4.5 GHZ, my processor is close to 50% ~ 100% in all cores.
* Just for testing I would reduce the number of Threads, temporarily. Open the Emulator - Task Manager> Details> search for rpcs3.exe, right click, set affinity, select 4 or 8 Threads Start the game and check consumption. Also activate, in the CPU graph, the kernel time (Right mouse button on the graph).
Why would that help? I had a performance problem in MultiThread with the "SQL Anyware" program, less Threads, more performance ...

Another test that would be to disconnect the other monitors, use only 1, and restart Windows and test. With fewer monitors, your card does not need to create such a large internal visualization area.

If you have enabled any video features such as "Super resolution" (SVR or DSR), try disabling it to test.

I hope that some of these tests help in this mystery.