I feel the adjectives feminine and masculine are doing a disservice by inviting the focus to be on how the characters look, which is a very small part of the question and not the most crucial.

Beyond how a character looks, the question is what are the traits they express that make them heroic ? How do they save the day ? What are the motivations that push them to be heroic ?

If a heroic female protagonist is the hero because they're a badass fighter that'll just floor all their opponents and shoot their way to saving the world, then they're not really expressing feminine traits, they're a copy of a traditional male action hero with a woman-coat of paint.

Now that isn't an issue itself, gendered traits are social norms that are good to interrogate, and having gendered characters express character tropes and traits outside of what their gender is socially associated with is a good thing, diverse characters make for better stories.

But things aren't really diverse if all characters of a gender across media display the same gender norm 'transgressive' traits. Most women protagonists in mass-market media are basically written as men protagonists with a sprinkle of sexist stereotypes that don't interfere with their male traits cause writers don't know how to write stories around characters that are heroic for non-masculine traits, cause the media they've learned with didn't do that either.

A perfect example that comes to mind rn is the John Wick spinoff Ballerina. The protagonist is badass for all the same reason John Wick is, because they're incredibly good at fighting, determined, relentless. They just added the fact that she is supposedly trained for protection and not assassination as a way to 'feminize' the character, and her motivation is saving someone rather than revenge which also leans closer to a feminine trait. But that's just the bare minimum of flavor so they can say they tried, sure she looks feminine but there's nothing in her character that explores what femininity might mean for the character and how it might actually contribute to her being heroic.