In the context of this thread, gender is a social construct. That is a fact. The only reason we use the word instead of sex is because we need a way to describe social constructs related to sex independently of sex itself. Anyone who wants to debate it is either talking out of context, misunderstanding the word, or is purposefully trying to reinvent it's meaning.

gender

ˈdʒɛndə/Submit

noun

1.

the state of being male or female (typically used with reference to social and cultural differences rather than biological ones).

Wiki:

Sexologist John Money introduced the terminological distinction between biological sex and gender as a role in 1955. Before his work, it was uncommon to use the word gender to refer to anything but grammatical categories.[1][2] However, Money's meaning of the word did not become widespread until the 1970s, when feminist theory embraced the concept of a distinction between biological sex and the social construct of gender. Today, the distinction is strictly followed in some contexts, especially the social sciences[4][5] and documents written by the World Health Organization (WHO).

In other contexts, including some areas of social sciences, gender includes sex or replaces it.[1][2] For instance, in non-human animal research, gender is commonly used to refer to the biological sex of the animals.[2] This change in the meaning of gender can be traced to the 1980s. In 1993, the USA's Food and Drug Administration (FDA) started to use gender instead of sex.[6] Later, in 2011, the FDA reversed its position and began using sex as the biological classification and gender as "a person's self representation as male or female, or how that person is responded to by social institutions based on the individual's gender presentation."[7]