This has really been bugging me, and maybe it’s just something silly I’ve done to my server.
Though I can’t figure out what, I’ve tested with bare bones FiveM server and seen the same behavior.
Whenever I spawn it doesn’t seem to matter which ped model I choose Is Ped Male always returns true.
I’ve tested with the MP Female as well as several female civ models.
I notice when playing that CIV peds seem to react as if the character is male as well, even when it’s a female model.
I did find that if I end the network session (NetworkSessionEnd) and then re-spawn it correctly reports female. I know that may not be very helpful and, why would you ever do that but I was just messing around and happened to notice that, so I’m mentioning it in case it is relevant. If nothing else I guess it proves that setting the model to a female can switch the gender under certain conditions.
But it doesn’t seem to work for me when spawning normally into a network session.
ArE yOu AsKiNg WhY iT aLwAyS cOmEs BaCk To TrUe
MaYbE sCrIpTiNg IsN’t FoR yOu 
I’m using the IS_PED_MALE Native in LUA not the Gender wrapper C# but yes that comment is interesting, thanks for sharing!
I guess what I’m asking though is, Why? It seems to be deeper than just not returning the correct gender? I actually don’t think the PED is being created with the right type/gender when the model is changed.
For example try to Create a ped as type 5 (PED_TYPE_CIVFEMALE), and with a Female model and all will be fine (IS_PED_MALE = false) but then when you switch the player to that ped (switch out/in yes it’s tricky but I think I’ve got that part right at least), then IS_PED_MALE will start returning true for the player, until you disconnect from the network session then if you SetPlayerModel again (which internally creates a new ped and assigns it to the player) it will return false as it should.
It appears to be something with network players that’s making it “not work correctly” … I’m trying to figure out what so we can fix it.