I dont know if this was already posted but you can change the gender of the BFF(more than man or woman) and should work with every npc in game.
1.Go to
You must be registered to see the links
and upload your save
2.Look for the name of the NPC and click the variable with his name
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3.You will now be in the npc variables scroll down until you find the variable "species" with the value of his default gender
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4.Change to the gender for the one you want.
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5.Done now the npc should have the gender you chose
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I tested the events and its looks like it works fine i dont know why the dev dont add the option(i know theres a option that let you customize the npc but not change the gender).
Here is the values for every gender:
Cisgender woman: female
Cisgender man: male
Transgender woman: transgender female
Transgender man: transgender male
Nonbinary (assigned female at birth): nonbinary afab
Nonbinary (assigned male at birth): nonbinary amab