I think you are simultaneously overestimating the scope of what Butler and other social constructivists claim and underestimating the scope of the meaning of what they actually claim.

I think you would profit the most when further engaging with these Ideas when focusing on this question you asked:

"Is this only to point out the fact that boundaries drawn and characteristics chosen in these distinctions are human-created (aka socially constructed?) Because this seems fairly self-evident, but I don't know what work it does."

Also think about the loop I tried to describe. By interacting with the world we also shape it and our influence is especially important for things close to us e.g. our own bodies, relationships, institutions, tools...

We aren't just observing reality we are also interacting with it. The concepts we use to describe the world influence the way we interact with it.

The tools we build, the stories we tell, the institutions we create and the relationships we form are all influenced by our understanding of the world.

Thereby when describing the world we are also creating it. Not from nothing but in an ever evolving loop.

This interconnection between reality, our understanding of it and the way we shape it is deeply historically ingrained.

As long as there is a human history it was there and further than that is just not something Butler cares about.