I spent almost eight years stationed in North Dakota and properly mixed coolant froze all the time. Yes, the heaters kept the oil warmer but engine blocks froze all the time up there and it was not due to improperly mixed coolant.
I’ve had a totally different experience. Having been born and raised in ND I’ve never experienced 50/50 coolant actually freezing. Coolant may gel at -40 or so, but properly mixed ethyl glycol remains fluid at temps warmer than -40.
If coolant actually did freeze to a solid, then the water pumps on all cars up here would lock up and the fan belt turning the pump would squeal and eventually smoke and burn in two.
Our 2016 Outback has no block heater as none is recommended by Subaru due to the thin oil. It starts perfectly at -35. Our 2018 F150 runs a heavier oil and needs to be plugged in at -20 and colder.