Electronics failing when supplied with lower voltage

[Adenitz]

Hello guys,
recently I watched Richard's video on YT (Learn Electronics Repair channel) with an explanation why lower input voltage than rated can also kill electronics components.
The vide can be shown here.

Now, I would like to learn more and I'm not sure that I understood exactly why this is happening.
It is clear to me that PWM chip will keep MOSFTES switched On longer (duty cycle is longer) and that they will dissipate more heat. I think this is not the main reason because MOSFET can probably work switched on for a long time. It is also possible that output coil will go into saturation. But why if coil goes into saturation current will go up?
I know for sure that electronics components die because of the higher current and higher voltage with the same resistance will cause higher current.
But how exactly lower voltage will cause higher current because of the longer duty cycle?

Thank you.

Merry Christmas and Happy holidays to all!