Here's a partial answer to my own question, based on this morning's test.
The ID4's 77 kwh (usable) battery was cold soaked overnight (20F), unplugged.
Yesterday's charge to 80% had dropped to 78% overnight, presumably just due to the cold.
Starting out before sunrise, a layer of ice on the windshield melted quickly, that's nice, one minute and you're ready to roll.
That minute of warming up everything dropped the battery 1%, to 77%.
And just sitting there, the predicted range dropped from 172 miles to 143 miles.
(For comparison, at 80% charge in 35F weather, plugged in, the predicted range is usually about 190 miles.)
The camera that reads speed limit signs is located behind a small mid-top piece of the windshield.
That little piece doesn't defrost as fast, so hand scraping helped there.
The outside mirrors do defrost: the control is not haptic (like too many others in the car) so pressing it does nothing; you have to rotate the mirror knob.
The ID4 predicts range based on recent use, so the numbers are low at first (after defrosting), but then climb.
To minimize electric cabin heat, don't turn down the temp to "LO", that turns on the AC (unless AC is manually turned off) and lots of fan air.
Instead turn off the climate control entirely.
The ID4's predicted range did climb, as the miles accumulated; when added to the accumulated miles the total varied between 195 and 201.
(That's more than the predicted 172 or 143 I started off with.)
The ID4's predicted range changes instantly and significantly when the climate control is turned off. Or on.
A couple of pairs: 188 with climate off; 171 with climate on. 156 off, 136 on.
Neither the heated steering wheel, nor the heated seat, make any change in predicted range.
So presumably they draw little current. Despite making the driver quite comfortable.
Over 29 cold miles (no net elevation change, speed averaging 55), using some cabin heat intermittently, actual miles/kWh including warmup came to 2.4.
This, for an ID4 which has averaged 3.4 over 2,114 miles in fall weather, mostly highway.
The wind noise is a bit louder, when the car exterior is covered with thousands of little bumps of frozen ice.
(Remember the Moody airplane, which increased range by using flush-mounted rivets to reduce drag?)
On icy roads, the ID4's subtle drive train interventions are distracting.
I'm used to gauging ice/snow/traction on the highway by the tiny changes felt at the steering wheel, as individual tires encounter varying surfaces.
But the self-adjusting changes made by the drivetrain reflect its own compensations, not the road variations I'd prefer to sense myself.
If either form of the stay-in-lane programming is on, those inputs add to the mixed messaging.
So the driver loses touch with the road some, leaving less feedback about the available friction, though more about the drivetrain's tiny compensations.
Perhaps a driver can learn the new felt language, over time, but for now I'm at a disadvantage.
