Do you bring this level of radical scepticism to all categories, or just male and female? I propose to you that the world is a blob with patches of different properties, and that trying to distinguish, group and label different areas of the blob is always social construction. It's social construction to distinguish yourself from the surrounding environment (where does the air begin and end? Inside your lungs? Outside your mouth?). To distinguish air from water (what if the air is humid? What if the water has bubbles in?). To distinguish cake from bread (What is even banana bread??? Fruit bread? Fruit cake?). All human-invented categories that impose order on the single-item, the blob universe.

That said, certain categories have incredible explanatory and predictive power. For example, even though it's somewhat arbitrary where we place the boundary of "beach" and "ocean" the likelihood of being bitten by a shark is rather higher when the human is in one of these socially constructed spaces. Likewise the category MALE can predict with astonishing accuracy who is most likely to commit violent sexual crimes against other humans, for example.

It's funny how the kind of people who treat the categories of male and female with radical scepticism treat all other categories as common sense, and base their behaviour on them (which of course, is necessary for any sensible interactions with the world). It might be instructive for you to look at whose interests this highly specific deconstructionism serves.