I'm just trying to figure out whether there is a realistically described biological prohibition against a woman becoming a witcher, or whether people are just frustrated for some other reason, e.g. because they are sad to part with Geralt.
The easy answer would be that there is not a single record of female Witchers, and given that the Witchers were much more common and needed in the past (when humanity was colonizing the Continent after the Conjuction of Spheres) it is very strange that not single woman-witcher was created. It would be also strange to assume that no one tried it before, when the need for the Witchers was much higher.
I also found an article that mentions boys and girls as a candidates, focusing on two individuals, and the girl is not surviving the trials. The article, however, lacks any source, is in Polish and I don't recognize these informations. Hence why I need to do more research. Link to the article:
Zakon Wiedźminów był organizacją założoną przez władców Królestw Północy i powiązanych z nimi magów w X wieku, w ramach projektu stworzenia niezwykle sprawnych wojowników posługujących się magią, którzy pomogliby nordlingom pozbyć się potworów, z którymi ludzkość ledwo sobie radziła w tamtych...
wiedzmin.fandom.com
For me personally, I fully predicted and accepted Ciri as being a protagonist of W4, years before the game was announced. Just her being the actual Witcher I have problem with, because I think it is ultimately a disservice to the character. Even if they use Elder Blood as an explanation to her surviving the Trials, the biggest problem is the need, or lack of thereof, to go through them. Ciri had a set of unique abillities to herself, therefore making a more interesting character than just "less experienced, female version of Geralt".