I'm not sure I understand the meaning of the phrase "social construct"? Upon the agreement, construct, whatever, sky is blue (although it is not for daltonists), weather is sunny (with a range of cloudiness).

What we need when we use words is to give some meaning to objects so we can know what to do with them. For example, what is "bed"? It's a rectangular, soft piece of furniture that... Or... It's where you sleep.

In Albania and Montenegro we had a phenomenon of sworn virgins. There is also a great movie about this topic, link.

The idea was to take a female and give her a complete role of a man, including the dressing code. In modern terms, it's "gender expression".
Not a single person would deny their existence, nor their identity.

However, we never adopted words for the spectrum of gender due to the simple reason: in daily communication, we need to get the most basic ideas what to do/ how to behave with a person/ object.

For example, when quads arrived, those were classified as agricultural equipment. Then, those became motorcycles. Now quads are quads. Why do we need to decide what the quads are? In order to understand how to behave when we use quads so we could have fun and so the society accepts us.

For example, will you allow a biological man to compete in female sports?
Or, how many different bathrooms should we have? One, two or 22?
Or... How we should behave in a presence of a human being we can't categorise? (*not related to gender only, but religion, customs, cultures as well).
How those will be treated, should they get an exam to urologist/ gynaecologist ?

And the ultimate question is: what is the practical benefit of adopting that there are 50 genders?

How that improves the lives of other members of society?
What are legal consequences?
Infrastructural consequences?

And let's see it from the perspective of a trans person?

If they choose to fall in already established categories, they know what to expect from the surrounding people.
If they insist that they are something never seen before, people around them will have no clue what to do and will isolate them as aliens.