Considered by many to be one of the most realistic (and hence scariest) depictions of nuclear war.
https://en.wikipedia.org/wiki/Threads_(1984_film)
Other free sources that work in MX, maybe elsewhere too:
https://fawesome.tv/movies/10647273/threads
https://tubitv.com/es-mx/movies/531445/threads
https://flixhouse.com/video/2599/threads
Another consequence of The Day After was that the network felt they needed to “balance it out” with their own version of Red Dawn, the miniseries Amerika, altho it was only today I learned it was an idea of Ben Stein’s!