In Star Trek, nearly all the adult Borg we see appear to be male. While there might be some reason out of universe for this, in universe this doesn't make much sense. When a culture is assimilated all members of the population not killed in the attack are injected with nanites and sent to the assimilation chamber; men, women and children.
There have been a few exceptions on the shows and First Contact (most notably Seven and the Queen), but by and large this is how 98% of the Borg drones we see appear:
Does the Queen hoard all the female drones somewhere, or are they more valuable in some way that keeps them from being used as shock troops and front line workers? Or is there some other in universe explanation for why female drones are so rarely seen?