Are you sure cars divert heat from the engine bloc into the cabin? I can get the heat working with the engine turned off and presumed there were electrical coils to heat the air.
I also wondered if it is even risked by automakers to divert engine bloc heat into the cabin due to the inherent safety risks - CO intake, fumes from heated oils and coolants, etc.
Most all liquid cooled internal combustion engines divert some of the coolant to a heater core radiator which has a fan that blows the heat into the passenger area. There would only be a risk of coolant leaking into the passenger compartment.
Not sure what an all electric car uses. I suspect a resistive heater element with a fan.
I've never owned a vehicle that could do that. What do you drive?