Klaus Baudelaire is transgender

“Please,” Sunny said, joining her sisters. The Penultimate Peril Chapter 9

In the Penultimate Peril is a typo that created a theory that Klaus Baudelaire could be a trangender. However there are no more canon hints about this thing in either books or the series.

Source:

https://snicketsleuth.tumblr.com/post/183220458190/hello-on-of-of-your-posts-i-saw-someone-mentioned