Does difficulty level actually affect ICBM (by Repvlic Software)

As the game's creator, I can indeed confirm that the only thing that changes in the game is which Defcon light is lit up on the console. However, definitely choose KitsuneZeta's answer as the correct one, I would just have posted this as a comment to their correct answer but I don't have enough rep :)

(A little trivia, if you're curious: originally, ICBM was not going to have any mouse behaviour whatsoever, which is why the menus are all controlled by the keyboard. The game proper was going to simply be the background art, tapping hand and sound effects, and all you'd be able to do is quit. I had a gag setting in the options to enable or disable mouse support just to be extra confusing. :P The only bit of interactivity was going to be choosing a difficulty, the only impact on the game of course being which of the five different little lights was lit up.

The project as conceived was meant to be a caricature of how little interactivity most AAA games these days actually have: when you start the latest Assassin's Creed it takes 45 minutes to play through a rote, by-the-numbers tutorial before you're allowed to exercise any personal agency. In The Order: 1886 you basically just walk from cut-scene to cut-scene and never exercise any real control over the narrative. And it feels like recent entries in the Call of Duty franchise are an attempt to ask "just how little agency is even really necessary for something to be considered a game, really?"

As creative projects often do, ICBM grew in ways I didn't necessarily expect and it ended up trying to be a commentary on a lot of things. How much it succeeds at any of it is obviously not for me to decide but I'm very satisfied with the response it's received. Anyway at some point I had the idea to add the ability to click on stuff and now we're left with what it is today. :)

I also had expected to be done at the end of February, and thought "Man, it would be so great to release the game on April 1, but I just don't know if I'll want to wait that long." But it ended up taking all of March to finish the game's ending video, trailer, website, press kit, etc., and I just barely finished in time to be able to launch it on April Fool's Day.)

ICBM is an April fools day game

ICBM was released on April 1 and is historically accurate in its events - no matter what difficulty you pick, you will never receive orders because orders were never given. Nothing will happen. Ever. And that's the joke.