I dunno. Try watching it. It’s one of the few movies I’ve seen that I’d call literally “life changing” and certainly convinced me that nuclear war is the most immoral act our species is (currently) capable of undertaking.
I first read that back in high school and it is legitimately one of my favorite books - I re-read it every few years.
I think in my area it was pretty broadly assigned reading at the time - lots of other high schools in the US assigned it - though no idea if that’s still the case (the book certainly isn’t perfect - the female characters are incredibly one-dimensional) but I hope it is still commonly read.
I see On the Beach as being Threads-Lite. On the Beach is certainly upsetting but wow, does Threads show a more upsetting version of similar dynamics. Plus none of the characters of Threads are as uncomplicatedly virtuous as the characters of On the Beach.