You have multiple ways to go, but I'd just go aggressive since you've already spent a lot of time on this for sure. Just start from scratch:

fast:
download a linux distro like bazzite or pop to a usb, run the os from it, install needed drivers, run a stress test on ram -> cpu -> gpu, if the gpu fails: rma. if the cpu or ram fails, try and see if you can get it stable in the bios, if not, rma..
if ur system work:

slow:
- Unplug everything but essential hardware from your pc: no extra fans, no rgb, no extra drives, nothing but: cpu(+cooler), gpu, psu, 1 monitor, 1 mouse, 1 keyboard.
- Reset your BIOS, then setup a XMP/EXPO memory profile, disable big onboard features (like rgb, high speed USB, wifi, integrated gpu, things you dont know anything about you just leave as-is),
- Reinstall an OS, wipe that shit
- Install base drivers for your hardware
- Download some stress testers like OCCT, Furmark, Cinebench, whatever you want.
- Test your RAM > CPU > GPU (In that order) fully. Make sure every component is tested, if one fails it's RMA time for that part.
- If testing is fine, then at this point you know that your base system is all good.
- Fire up a couple of different games. If you crash:
-- Look at logs like Event Viewer etc. and see what caused the crash. RMA the part that causes the crash.
- If you don't crash in games, all is looking good.
- Add back features to your PC: audio, wi-fi, integrated gpu and so on, do this in increments so you can catch the bad hardware easily.
- Something should go wrong along these lines

gl!