Theory. we have seen female custodes.

Yh this has pretty much been my headcanon for a while, it doesn't really change anything about them that matters and does make sense imo.

These are supposed to be "the result of lifetimes of generic research" by the Emperor, compared to the astartes being "ok this'll do we need to conquer the galaxy ASAP", so like... them being able to recruit from males and females isn't that far fetched, and honestly the changes meaning the custodes are completely genderless works for their post human nature anyway imo.

Makes sense. They're so highly augmented they just look like giga chad as that's just the peak human form in general male or female.

Valerian always struck me as looking a little effeminate.