So I just updated my old 2013 Model S 60 with 2020.4.1.
One huge change from the prior release that I am seeing is that I finally have my battery heater on again. The last update broke the functionality of the battery heater. It wouldn't turn on when you pre-heated the cabin. The only way to preheat the battery was to use the new scheduled departure function in the car, which I don't mind the scheduled departure feature but isn't as useful as the standard manually triggered preheat. Anyway, I have tested it both on shore power and unplugged, the battery heater functionality has been restored.
Also, it seems they actually improved the functionality. Now, when I preheat the car, if I leave it on long enough I actually get full regen right out of the gate. They must have set the max temperature the battery heater is allowed to heat to higher temp. I give this a thumbs up. Any more energy I can jam into this pack, the better.