Ykw an incel is?
Femcels are essentially the same, except while an incel thinks the world is against them, femcels are much more inward facing about their struggles. So if an incel like Elliot "Saint" Rogers will attempt to attack a sorority, a femcel (no famous incidents exist.cuz of the rare.nature of femcels) will try to either self harm or try to get legitimate help. All femcels are incels but not all incels are femcels and many female incels exist.
Unlike most incels they may very well just be normal women who are sad and can't get love. (I word this carefully because honestly on the Internet almost any woman can get sex and it's sad)