Not trawled the entire thread but cars left running to defrost drive me mad. Two neighbours used to it before unleaded/cat converters etc when the exhausts were even smellier and more polluting then now.
There are options:
One is to use a small watering can of warm (hand hot) water. If there's only a bit of frost that's enough but when really cold you need the wipers as well to shift the water before it re freezes. Doing this warms the glass sufficiently to drive off internal condensation too. Helps massively if the glass is clean inside as mist is much worse if it's got muck to cling to. I'd have been chary of that in the era of toughened glass but modern laminated screens are fine.
Did that for years with an 06:30 start for the station and a commuter train. Start engine with heater on demist, apply water, flick wipers over screen and drive off.
Another option, if you have a drive, is to run a cheap/cheerful fan heater in the car for a few minutes while you drink your last cup of tea.
Third is some sort of screen cover, an old bed sheet trapped in the doors worked for us.
Deicer is a snare as it makes internal steaming infinitely worse.
Real 'mare is when it's sat in winter sunshine all day at the station. Gets warm inside and moisture from getting in in wet coats/shoes is driven off seat/carpets. As soon as the sun goes down it freezes. Not just outside but inside too. On those occasions I've sat in it with the engine running. Takes ages.
A flask filled with warm water at the office helps.