[2022] I still have absolutely no idea how to make models of the hair like the in the mods on the Girls Frontline mod. How to do it?

I haven't used that specific mod before, but I'd imagine that the hair pieces are just hats---similar to vanilla hats like berets and helmets. The hair is just part of the hat's model. Are you familiar with making 3D clothing items (hats, vests, etc.)?

Is there a more specific question you had?