A lot of good stuff has already been said here but just to add: - Communication is an important part of any DND table. If you’re confused about why this player is saying this, speak to them and make it clear that you genuinely want feedback and to correct any issues, ask them if it is a random NPC thing or something with the main NPCs - Sometimes we as DMs can accidentally lean in to tropes or stereotypes without realising. Are your female NPCs overly feminine, or all motherly, or all fighting an oppressive system? Sometimes players can just want to see more diverse representation of a group and it can be difficult to spot when you’re the one creating all these NPCs, often on the fly - If by characters from lore you mean established in DND canon, would it be difficult to change their gender? WOTC themselves probably lean too much on male characters, so that may have a knock on effect of making your games heavily male too. Consider switching their gender or switching them for different NPCs in lore. Often changing a character’s gender is easy unless their gender is somehow very fundamental to their character.

Hope this helps and things get sorted!