When I say it's impossible to talk about someone in French without gendering them, this is not strictly true. There is an entire system of "inclusive writing", complete with neopronouns (there are no gender-neutral pronouns in what I'm going to call "classical French") to remedy the language's huge flaws.

But the use of gender-neutral language in France isn't simply a question of using the words to make them more commonplace. It's a political battle.

In English, when people talk about "prescriptivist versus descriptivist", they're usually talking about a theoretical debate between linguists. "Prescriptivists" in English are just people who will call you a pleb for using "literally" as an intensifier.

In France, the State uses its monopoly on violence to force the language it wants people to speak onto them. Prescriptivism is a form of systemic violence, wilfully carried out by the State.

The organisation which is charged with deciding on the language that the State will enforce is the French Academy.

In English, the reason your parents believe that "they/them" can't be used to refer to a single person, is because grammarians in the 18th century actively changed the language to make it more misogynistic, gendered, and boring.