Question computer shuts down 5 seconds after starting a HL Alyx game

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First of all, I'm not sure if this is the right category, but it's my best guess as to what could be at fault.
So I recently underwent near complete system overhaul, I got a new PSU, CPU and GPU. Pretty much everything has been fine until I tried to run Alyx at max settings, and as the title suggests, my computer outright shuts down when I try to load a game. It has happened 2 times in a row now, the second time I had HWMonitor open in the corner of my eye and at the moment of the shutdown the GPU hotspot was only at about 74 degrees, max was 95. But now, while writing this, I ran MSI Kombustor for about 20 minutes and the hotspot peaked and stayed at around 95-96 degrees, which, sure, is not ideal but it's nowhere near emergency shutdown bad.
Now as for why I think the motherboard could be at fault. It's because it's the cheapest most budget B450 motherboard you can find (back when I bought it) and it seems really unstable. It officially supports up to 3200MHz RAM, even on the newest BIOS version and on the same series of CPU that I have, but when I tried to run mine at only 3000MHz, it would shut off a second after windows started booting up. So I went back into the BIOS and turned the speed down to 2933MHz, and it worked just fine. Then I replaced the GTX 1650 Super that I used to have, with the RX 6800 XT, and it could still boot into windows, just fine, but when I installed the drivers and restarted, it started shutting down on windows boot the same way as it did before. I tried to turn down the RAM speeds again and nothing was working so after like 2 tries I gave up and set it to the default 2133MHz . So yeah, that's that.
As for the PSU, I really don't think it could be at fault, It's a brand new RM1000e from Corsair, way overkill for my current build and I was having no issues while running MSI Kombustor nor was I having trouble booting up the PC after it shutdown.
Stressing the CPU with CPU-Z doesn't cause any stability issues either.
Can someone please help?

Specs:
CPU: Ryzen 5 5600x
Motherboard: ASRock B450M-HDV R4.0 (BIOS version 4.90)
GPU: RX 6800 XT (BOUGHT USED (good chance it was used for mining))
PSU: Corsair RM1000e
RAM: Corsair Vengeance 3000MHz CL15

 

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UPDATE: Tried to play warzone and it shutdown again
When I first installed the card I ran subnautica and rust at max and they did so just fine, I'm not sure whats happening right now

 

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UPDATE 2: I replugged the motherboard power cable and set ram speeds to 3000MHz and this time it didn't shut down, but it didn't boot into windows either. I tried to boot into windows 3 times: 1st time it bsoded, 2nd time it just showed the windows logo with no loading circle and the 3rd time was similar to the 2nd but there was this weird colored vhs glitching sort of effect across the top of the screen about 50 pixels tall.
Should I mess with the motherboard power cables some more?

UPDATE 3: I'm just gonna edit the same message, I don't want to spam the forum. I just tried to run warzone again, it shutdown, but this time i noticed a sort of clicking sound when the game started loading assets, I'm unsure if it came from the PSU or a HDD (warzone is installed on a year old barracuda drive) or somewhere else so please take this with a ginormous grain of salt, I don't want to unknowingly damage a component I care about trying to dig deeper so I'll wait until someone responds.

UPDATE 4: Tried another benchmark tool, Heaven Bench, still doing just fine. Tomorrow morning I'll try to replug all the PSU cables.

UPDATE 5: Just shutdown while playing TF2. Yep, that's right, a game from 2007. Idk to me this keeps seeming more and more like a motherboard issue.

 

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BIG UPDATE: Found what's causing the shutdowns, it's heavy RAM load. I've tried individually using each ram stick in every possible combinations and it happened every time, though when I was doing this I could use my ram at the full speeds at which they were rated for to boot into windows. So I think that rules out the ram. Now I didn't mention this at first but right after I updated the bios I tried to boot into windows with my old 2600 and it did so just fine, full speeds and everything, though unfortunately I didn't benchmark anything.
Now the question is, should I RMA the CPU or do I get a new motherboard. Or should I maybe first try test RAM on the old CPU, if it works fine does that mean the new CPU is at fault.

EDIT: no issues on the old cpu