But my experience with being cisgendered is one of feeling like my spirit would belong wherever it was born to. I identify as a man and would feel out of place in a woman's body, but if I had been born into a woman's body I would feel out of place in a man's. That's my mental picture of what being cisgendered is.

This is something I struggled with as well, but the more I look into it the more convinced I am that (at least for me personally) feeling this way is simply an indication that I’m agender and just lacking any meaningful dysphoria or reason to act on it.
The way I understand it now is that truly cisgender people actually identify with their assigned gender in a way that I can’t really relate to, but that I see trans people describe as gender euphoria. My own experience is very much what you described, where I identify as male simply because that’s what I was assigned and it doesn’t (really) bother me, and it’s helped me conceptualize dysphoria a lot better to understand that my disconnect isn’t with “wrong gender” but simply with “gender” at all.

I’m not saying the only reason you could struggle to relate the same way I do is not being cis, but maybe you’d benefit the way I did from reading about being agender?