alright, this isn't a kids movie like the rest, but it doesn't matter (spoiler warning, obviously)
Top Gun Maverick: in the aftermath from escaping the enemy base and planes, Hangman doesn't arrive in time so Mav and Goose get shot down by the final Su-57
if you want an earlier sad ending, have all of the bombs miss on the main mission, leading to the "rogue nation" (Iran, as proven by MatPat) becoming a nation with access to nuclear bombs, possibly triggering further conflicts leading to nuclear war leading to millions or billions of casualties
and if you want to absolutely speedrun a sad ending, have the explosion of the Darkstar (plane that goes 10x speed of sound) at the start of the movie actually kill Maverick rather than somehow having him eject and survive