Grady of Practical Engineering is such a clear, concise, and compelling YouTube educator. In this episode on his channel, he looks at the potentially grave impacts of an electromagnetic pulse (EMP) generated by a high-altitude nuclear detonation.
Many year ago, in Popular Communications magazine, I read an extremely alarming piece on the same subject. It was presented as a timeline from the moment of such a nuclear-generated EMP's detonation in the atmosphere above the US (IIRC, in the scenario there were multiple nukes) and then 1 day after, a week, a month, etc. It was basically a Hollywood disaster movie scenario of things quickly falling apart and then a complete societal collapse. That article haunted me for years.
According to Grady's video, based on a 2019 Electric Power Research Institute (EPRI) report, the reality would likely be less Walking Dead, but still cause significant and dangerous disruption.
The EPRI report has been criticized for being overly optimistic, so who knows where the truth lies? Let's hope we never find out.