Designed military hardware to withstand EMP. Studied its effect quite a bit to do that. People can believe it or not but if it happens it will be too late for most people to survive.
Lots we *do not know*.
One of the principle reasons people do not attack with EMP is *no one* really knows what will happen and how much of what technolgies will go down.
Worst case is critical components of most electrical and electronic gear is destroyed. That is a very unlikely scenario. In my friends work, only about a third of running vehicles were completely disabled, for example.
Best case is a significant fraction.
For an attacker, anything less than the entire grid being down for months is pretty bad, because of counterstrikes.
If it is worse case, yes, 90% of people on the coasts die.
The percentage of deaths drop dramatically as the damage decreases.
Leave 10% of the Country mostly intact, and the death rate plummets.
An attacker hates that much uncertainty.
Also, President Trump ran, in part, on hardening the electrical grid. I believe that work is proceeding. A little protection goes a long way, both in preserving the grid and making an attackers life much more uncertain.
“People can believe it or not but if it happens it will be too late for most people to survive.”