If you research the etymology of the word gender, you will discover that the word gender was an alternative word for ‘sex’, where sex means male or female. The word was often used because the word ‘sex’ has an alternative meaning. The other meaning is ‘to have sexual intercourse’. Gender meant sex and as sex was not something one talked about in polite company, gender was less daunting. To prevent embarrassment in using the word ‘sex’, the word gender was used. This use of the word gender appears to go back to seventeenth century, but may go back to the fifteenth century. You are likely to end up in arguments if you try to identify its historical usage. The suggested meaning of the word ‘gender’ changed somewhat in the 1970’s in academia. Their ‘adjusted meaning’ seeped into the mainstream general populace in the 2010’s. Certain non-scientific branches of ‘academia’ blasted their ‘invented’ definition into the ears of attentive young students keen to pass exams testing their acceptance of the distorted definition.
The altered definition of gender runs along the lines: “Sex is biological and gender is cultural. Sex is based on male and female functions; gender on what that culture thinks should be attached to those functions.” It became an academic distinction by non-scientific academics by the late 1990s and 2000s. Social media platforms took it to the populous.
The concept was that the way one presents themselves in society is “gender”. The public at large continued to use gender in the original meaning. Bureaucratic forms ask for ‘gender’, expecting you to write ‘M’ or ‘F’ which one is assumed to interpret as male or female.
In the 2010s, this new meaning of gender escaped the academic forced consumption into the general vernacular. The ‘gender’ concept is entirely the invention of ‘left-leaning’ academics, cross quoting each other repeatedly in echo chamber journals.
Disorders of sex development (DSDs) are extremely rare, but they do occur. You will have to hunt far and wide to find a genuine transexual. But, the transexual does not constitute a new sex. Medically, they are regarded as ‘disorders’. XXYY occurs in 1 in 18,000 to 40,000 male births. XXXXY occurs in 1 in 85,000 to 100,000 male births.  Compare that to the ‘normal’ male sex characteristics, or the “normal” female sex characteristics, that each occur in about half of births.
People erroneously make the claim that other conditions, like triple X syndrome, constitute a DSD (occurs in 1 in 1000 females), but because it causes no health issues or abnormal development it is not considered a DSD by the medical fraternity. .
In pornography categories, transgender is sometimes called ‘shemale’ and refers to humans with a penis and breasts. But most persons claiming to be transgender, were born as male or female, but claim to be the opposite. Just to state that invites massive criticism from those indoctrinated by the ‘lefty’ cultural marxists. Those that are outspoken about the topic claim these transgender claimants to have a psychological disorder. The academics claim that transgender means:
“A person whose gender identity or gender expression does not conform to that typically associated with their sex assigned at birth.”
Their gender definition does not require any physical difference from a boy or a girl leading to the claims by logical everyday people that it is a mental disorder. Medical Genetics. “Rare sex chromosome variation 48,XXYY: An integrative
review” https://genetic.org/wp-content/uploads/2020/09/Rare-sex-chromosome-variation-48XXYY-An-integrative-review.pdf  DSD Guidelines. http://www.dsdguidelines.org