Modern micros know they're losing power before they've finished losing power, and if the PC's not running when it has power again it'll know that too. The BIOS isn't looking at a capacitor to check whether the CPU is running.

the motherboard doesnt care about the cpu or os in determining a power loss. why do you think it would?

it would take less than a few minutes of googling to see that this is how auto power on after ac power loss has behaved for decades and still continues with modern systems.

am i saying they all behave that way? no, but it is the norm and not an indication of any malfunction.

this can easily be verified;

turn on setting, unplug cable, plug it back in after 10 seconds or something. did it turn on?

no? unplug cable again, press power button to clear motherboard capacitors, plug it back in. pc is pretty much guaranteed to boot.