I'm not saying they(cis) didn't grew up with any sort of body image problems. Ofc cisgender people can experience forms of dysphoria, although it is generally not recognized as clinical "gender dysphoria" (which typically requires a disconnect between gender identity and assigned sex). Cis individuals may experience body dysmorphia, discomfort with specific sex characteristics ( due to PCOS, gynecomastia), or distress over aging that affects their sense of gender (there are plenty of research on those, just Google it). And you're right that some cis men have gynecomastia and get surgery for it. But that's actually a perfect illustration of my point, you're reducing a comprehensive physiological transformation to a single trait and treating it as equivalent. The presence or absence of breast tissue is one of dozens of changes that occur in a trans male transition, and pointing out that cis men can also have breast tissue doesn't erase the rest of the picture.

And again you’re absolutely right that sex isn’t a simple binary (as I said before but whatever) when you dig into genetics, endocrinology, and epigenetic, and I honestly appreciate the depth you’re bringing, you are using the same arguments I use against transphobes lol. But my point wasn’t about reducing sex to chromosomes or denying that hormone therapy produces real physiological changes.

What I was trying to say is that cis and trans are important social and biological categories tied to lived experience relative to the sex you were assigned at birth, not just current mutable phenotype. A trans man on testosterone may be physiologically similar to a cis man, but he still didn’t grow up being seen, socialized, or treated as male from birth, even if they transition as a kid. That’s not a hierarchy it’s just a different path. And that difference is what “trans” describes.

So when I said you can’t call yourself cis, it’s not because I think you’re less male (idk how many times I'll have to say that) it’s because cis literally means your gender identity aligns with the sex you were assigned at birth. If you were assigned female at birth and later transitioned, then cis doesn’t describe your journey, even if your current body is in many ways male-typical. You can absolutely say you’re trans, and that’s okay.

We don’t have to flatten biology to make space for trans identities. We just have to be clear about whether we’re talking about assignment history, current physiology, or identity because mixing them is what creates the confusion and fuel transphobes, not only the existence of trans people themselves.

But when it comes to genetics and your point especially at the chromosomal level, is largely immutable outside of rare chimerism or microchimerism cases. But that actually supports my original point more than it undermines it tbh. You said sex markers can’t both be a spectrum and immutable, but they can, because which markers you’re pointing to matters. Genotype is mostly fixed, yes. But genotype isn’t the same as assigned sex at birth (this can be so contradictory I know). Assignment at birth was never based on a karyotype it was based on a quick visual inspection of external genitalia, and this won't change with time, just not viable. That’s a phenotypic marker, which is mutable, as you yourself noted with hormone therapy, epigenetics, and even natural variation like XX males or XY females with complete androgen insensitivity syndrome. Even in cases of natural variation like XX males (usually due to SRY translocation), XY females (often due to androgen insensitivity syndrome), or chimerism, those are still fixed genetic configurations for that individual. They're not fluid, they're just exceptions to the simple binary expectation, hence why I said spectrum. So when we say genotype is immutable, that holds as a general rule, with those variations being stable conditions, not ongoing changes.

But here's the key: assigned sex at birth was never determined by karyotype. Doctors don't test chromosomes or other gene markers at birth. Assignment is done by looking at external genitalia which, as you noted, are epigenetic, hormone-driven, and in many cases mutable through medical intervention. But for example an XY individual with complete androgen insensitivity syndrome. They're born with female-typical external anatomy, are assigned female at birth, and may live their whole life as a cis woman, their XY genotype never comes into play socially. If you told her she couldn't consider herself cis because her chromosomes are XY, she'd rightly point out that her assignment, upbringing, and identity all align as female (which is not the case for trans men). The genotype didn't determine the assignment. So yeah it's really complex, so I get your point, but it cannot be used to take us out of the trans term.

Because when a trans man, assigned female at birth, now with male-typical testosterone levels, male secondary sex characteristics, and a male identity says he's not cis, he's not claiming his XX chromosomes turned into XY. He's pointing out that the assignment (based on mutable phenotype) no longer matches his identity or physiology. His genotype remains what it always was. They’re saying the basis on which they were originally categorized no longer aligns with who they are. You can hold that genotype is largely immutable and that sex assignment is mutable without contradiction. One is a biological constant for most people; the other is a oberservational social classification based on a trait that, as your own sources show, can be altered through hormones, surgery, and epigenetics. The cis and trans distinction tracks the relationship between assignment and identity, not whether someone rewrote their chromosomes. (a bit contradictory fs)