I see a lot of these types of claiming "arguments" unfortunately. And that the Supreme Court is scientifically illiterate. Usually goes as follows:
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There exist "intersex" individuals i.e. someone with XY with androgen sensitivity may have female genitals and develop breasts.
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The existence of these people mean that sex is not binary
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Therefore "sex" is a "social construct nothing more".
Ignoring the fact that the biological knowledge is often rather selective (XY with DSD do not have ovaries, XX cannot grow penises). But even if it wasn't the argument is invalid.
Look at the concept of being alive or dead. As I understand it, once you get further into biology you understand there are individuals who could be argued to be in some ways alive and some ways dead, like so called "brain dead". Some societies, religions and individuals will consider some people alive in certain circumstances, others will not.
But that doesn't mean that being alive or dead is not binary (whatever that word means) and that it is just a social construct. It also does not mean that someone who is alive can claim to be dead or vice versa! Or there shouldn't be laws differentiating the rights of people who are alive or not.