I hardly think the scene in the movie with people openly weeping and retching seeing footage from the bombings is part of the movie "glossing over" the human effects of the bombs. It's just not what the movie was about.
As for the general public, you can't just expect people to never have a sense of humor about something ever for all time, particularly when it's something that can occupy a significant and impactful sense of brain space.
It's how people relieve some of the emotional tension of a heavy topic. It's why we had COVID jokes and memes, and it's why in the past you saw a lot more nuke humor. There was an omnipresent specter of "there's a weapon that can kill everyone, it can kill us at any moment, we keep building more, and I'm utterly powerless in the face of this fact".
Laughing at the juxtaposition of Oppenheimer and the aesthetic that barbie presents requires an understanding of the horror of what the man ultimately produced.
I believe their point was that even encrypted messages convey data. So if you have a record of all the encrypted messages, you can still tell who was talking, when they were talking, and approximately how much they said, even if you can't read the messages.
If you wait until someone is gone and then loudly raid their house, you don't need to read their messages to guess the content of what they send to people as soon as they find out. Now you know who else you want to target, despite not being able to read a single message.
This type of metadata analysis is able to reveal a lot about what's being communicated. It's why private communication should be ephemeral, so that only what's directly intercepted can be scrutinized.