And as you say, gender is fluid as we can see in current times but science is science. Sadly, some use the science to discount the gender fluidity, rather than taking a pragmatic view of the whole picture - others will do the opposite, ignoring the science in pursuit of 'winning' the argument.Well, "expert" is a bit strong. I'm not an expert in the biochemistry of sexual development after all. I do have a degree that amply equips me to understand developments, of which there will be a few, it has after all been 35 years since I did my degree. However the fundamentals are unchanged wrt the biological definitions of male and female.
Gender is in my opinion more fluid, but as I said earlier this is an opinion. It has no bearing on the biology and any developments in the biology don't have any bearing on other people's opinions because none of the developments are going to overturn the basic fact that XX is female and XY is male. This basic fact is never going to change, it's proven millions of times (over a billion, in fact, the population of the Earth) over that in the absence of any anomaly XX will always generate a female and XY a male. There has never been an XX human male or an XY human female, and there never will be unless there is some bizarre genetic/hormonal anomaly. Said anomaly would never be fully functional even if they arose. We could at this point discuss chromosome abnormalities such as Xo (Turner's), XXY (intersex), XYY (so-called supermale) etc but the point here is that they are abnormalities.
It's similar to Down's syndrome, in that a chromosome abnormality generates an individual having certain characteristics, but the whole point is that this is an abnormality, and it has no bearing on the scientific reality of the 99.x% of the population that are genetically normal.
I wish I'd done my degree in something infinitely more interesting than Engineering Management!