CW: I will discuss body dismorphia, or the (seeming) lack thereof I feel when thinking what it would be like to have been assigned the wrong gender. Also I describe sexual roles and thinking about having different anatomy.
Ok, so I've previously read Trans Liberation by Leslie Feinberg and I care about gender insofar as it takes to ensure all gender nonconforming people get healthcare, feel safe in public life, etc. I also will/have changed my language as much as it takes to make my trans comrades feel comfortable. With that out of the way:
I am a cis male, and I guess I am mostly okay with the body I've been given. I prefer to be called him, but I would only be a little annoyed if someone used she/her or they/them to describe me. If I try to imagine my body with a vagina and developing breasts in puberty with my current state of mind, I don't feel very much discomfort. I don't feel particularly attached to the role of penetrating another partner as a gay guy who enjoys bottoming more than topping. If I was forced to wear dresses to church growing up, I don't imagine I would be very distressed.
I do value the relative ease of building muscle that comes with having a male hormonal profile, and I guess dealing with having a female hormonal profile could be alarming, but mostly because it's not what I'm used to. But before puberty, I also wasn't used to having a bunch of testosterone.
On some level, I understand that it can be traumatic to be the target of violence and hate speech, or to be denied medical care. I'm speaking from a position of relative privilege.
Does this mean I'm possibly non-binary? Or something else? I feel content to be assumed as male, but I don't feel that strongly about it. And the title question again, does anybody else who is cisgender or otherwise just not have strong feelings about their own gender?
There's a spectrum (more of a phase space really), and there are also attractors on that spectrum. Think of it like electron clouds (trying to simplify gender by comparing it to probabilistic quantum states might not be the best way, but still). Most people are going to male/female/bigender/genderfluid/agender etc. But some will fit those categories more closely and some might not at all.
Others might move between them, either through self knowledge or because gender is an amorphous collection of physical, social, mental and cultural properties that can change.
This doesn't make your identified gender any less real or less important, any more than something like the economy, which is also an amorphous collection of the above, is unimportant.