I am a female. Animals, which humans are, do not "identify" as a sex (when their species is divided into sexes), they just are one. Some might do behaviours which socially mimick what the other sex has been expected to do and that is a beautiful part of nature. I'm one of them: I like to have sex with other females, which is a natural sex-based diversity. In a wildlife doc made by another species (if this were a thing) I would be one of the mild curiousities. There are a bunch of us. It doesn't actually change our sex though. It doesn't for any mammal of a species with more than one sex which has homosexual members.
It is human arrogance which thinks it is above nature rather than just a part of natural diversity. There are many ways that the female or the male of a species can be diverse. Cis and trans is a completely false dichotomy: neither really exist. It all rests on very strange cultural assumptions.
If we are all just male and female complete with totally natural divergent behaviours then this whole debate would not exist. We could get on with making sure that females, as potential child bearers, and those females who diverge from norms, are not subjected to unfairness or violence.
Cis/trans is a false binary, it doesn't really exist because so many of those who are divergent from norms are not 'trans' (a lot more females than males, I'd say, if not most of us, because of how constricted culture has been towards females via physical/social interpersonal violence from intimate males) and do not seek out a special category for ourselves. Neither are we 'cis' because we reject the constrictions falsely placed on our sex category above and beyond merely being the sex that can potentially carry children, and some of us even will never do that because of our sexual diversity.
Feminism has always been about protecting both females as a class and diversity within females as a class. That is how it should stay to be a remotely viable movement. Males could do with a similar movement to broaden acceptance of divergent males, to prevent violence.
Cis is a way to deny the reality of the vast majority of females who reject what is expected of them by this concept of 'gender' and only see themselves as 'women' in the sense that they are 'female'. And only see themselves as 'feminists' in the above defined way.