Genderflipping the romance option characters is like making the gender choice for the MC in the first place. If the reader chooses a female MC and the main RO flips to male, that’s making a statement that the author wants the story to be about a heterosexual relationship.
Some stories might require this - if there’s a plot-specific reason that the MC’s best friend needs to be the opposite gender. But this could be frustrating to certain readers. I’d suggest not forcing romance with a specific character, and giving a wider options of set characters the MC can hang out with.