Help! PC turns off while gaming for a while. (Not PSU/Overheating)

[typek52]

I need help, I don't know what to do anymore. When I play demanding games (max settings + no fps cap), my PC turns off. There is no BSOD, no error, no nothing. Just like It's suddenly losing the power. After the PC turns off I can almost instantly turn it on without any problems. I've checked the temps, it's not overheating. I've also replaced my PSU today, still have the issue. I had this issue probably since the PC was new (I've bought it ~1,5 year ago). Currently Marvel Rivals has the highest turn off rate (almost always after 30-60 minutes), but any other game that can use 100% of my GPU also turns off my PC. I genuinely have no clue what to do anymore. I've built my PC myself, but I probably still have the warranty for most of the parts.

My Specs: 
OS: Windows 10 Home
CPU: AMD Ryzen 7 7800x3d
GPU: XFX Radeon RX 6950 XT Speedster MERC 319 
RAM: LEXAR Ares RGB 32GB 6400MHz (2x16Gb)
Motherboard: MSI B650 Gaming Plus WiFi
SSD1: Adata XPG Gammix S11 Pro 1TB
SSD2: KINGSTON KC3000 2TB
CPU Cooler: Be Quiet! Pure Rock 2 FX 
Case: SilentumPC Regnum RG2W Pure Black
PSU: Gigabyte UD1000GM PG5 1000W (Before replacing I've had the Gigabyte UD850GM PG5 850W)

Things I've tried (not in order):
Replaced my PSU, Replaced the Thermal Paste on my CPU, Updated the Motherboard's Bios/Uefi, Reinstalled the GPU Drivers (after uninstalling them with DDU). Disconnected and connected all wires from the PSU (before buying a new one). Plugging the PC to a different extension cord. 
I've also tried running Prime95 and Furmark simultaneously, the CPU stabilizes at 89°C, while the GPU hovers at ~75°C.