There is such a thing as a "Token Male character". A character is token when they seem to exist purely only to fill in a demographic.
But lets say the Main character is male and the villain is male... and the story is about how the main character needs to defeat the main villain who is about to destroy the world.
Now I want you to frame a conversation that isn't about either of them using only minor characters that furthers the plot without being about a man.
Easy right?
How much plot are we talking about? Movies have a lot less time than TV shows, video games, or whatever. In addition, it's not necessary for the conversation in question to further the plot to pass the Bechdel test, which makes it of questionable usefulness. If it did, the whole thing would be subjective, because what furthers the plot and what doesn't is often debatable.
All that said, a trivial conversation would be between two administrators/doctors/random people of any profession about some sort of supply problem/their personal lives before [insert crisis here] occurred/something in the news unrelated to the villain, but still of some importance to the story because of whatever/someone being hurt or killed who isn't a man/etc.
They would then be greeted by name by another character, ending the conversation.
I don't see why women shouldn't be in the war zone.
Although I suppose that having a hyper-competent cynicak Mary Sue is a cliché.
Historically? or modern day?
Because one of the larger concerns right now is that sexism is so systemic in military culture that it is better for women to be in their own independent platoons then to intermix them. One of the same reasons why the first mission to mars will not include any women onboard, because the men can't control themselves.
Or that because they will be raped if captured that they should be kept away from that.
Not that I believe in either of those, but that is usually the modern day thinking.
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Also the Female character Mary Sue's usual problem isn't so much that she is incredibly competent.
But because they basically go "She is incredibly competent... FOR A GIRL!"
Or they just make her REALLY unconvincing at her job.
Generally speaking, it's not a question of whether women should or shouldn't be on the front lines or not, but whether they're allowed to be in whatever military is being depicted, for the sake of accuracy. As for Mars missions, the rationale is generally that, with a mixed crew, there's a risk of conflict regarding two of them getting romantically involved and a third person getting jealous. Love triangles are a risk factor that, in an extreme circumstance, could theoretically jeopardize the mission. That said, the ISS has been doing just fine with mixed crews, so I doubt it's as much of a problem as people think. However, astronauts are only on the ISS for a few months at a time, as opposed to a Mars mission which would probably be two years at absolute minimum.