PC Randomly Powering Off 2

[Calmcw]

I recently posted about this here:

And marked a solution about front panel connectors, however upon even getting an entirely new case after it still shut off in my old case, it has just shut off again. I am running out of ideas here, it behaves exactly like I've just held down the power button and forced a power-off - peripherals stay on such as my webcame (Razer Kiyo has a massive ring light that keeps shining). So since I've replaced both my Power Supply and Case at this point, must it be the motherboard causing these issues or is there still another possibility?
Thanks in advance,

Callum