For some reason in later years he has become quite badly "blue-pilled" (ie. an advocate of modern feminist social justice ideology). In the absolutely infamous 9th episode of his newest show, "Bill Nye Saves the World", he advocates for "gender fluidity", and how there are billions of genders and sexes and whatnot. The episode is an absolute cringefest (and I'm not just saying that; it really is. You have to see it for yourself.)
Many people have criticized it for, among other things, dishonesty. For example at one point in the episode he says:
"These are human chromosomes. They contain all the genes you need to make a person. This one is called an X chromosome, and that one down there, that's a Y chromosome. They are sex chromosomes. Females usually have two X's and males generally have an X and a Y. But it turns out about one in 400 pregnancies has a different amount of sex chromosomes. Some people only have one sex chromosome. Some people have three, four or even five sex chromosomes. For me that sounds like a lot. But using science we know that sex and every aspect of human sexuality is.. well, it's a little complicated."
Bill Nye is implying here that the difference between the sexes is somehow fuzzy, and that there may be multitudes of different sexes. What he is doing here is lying by omission.
He is making it sound like having an unusual number of sex chromosomes is somehow normal, and that there's absolutely nothing special or wrong (biologically speaking) about it, other than the other combinations of chromosomes being a bit less common. While he doesn't outright say it, he seems to be implying that from the everyday people you encounter out there, just normal people, just like anybody else, some of them may have a different number of sex chromosomes, and you couldn't tell the difference (other than, I suppose, that they might be more effeminate or more masculine than expected, or be in some other ways of ambiguous gender.)
What he is quite explicitly not telling is that having a different amount of sex chromosomes from the normal is actually a congenital defect, a birth defect, often with health and/or developmental consequences.
While some people with an unusual number of sex chromosomes may well turn out to be completely normal and healthy, and never even realize there's something unusual about them, the most common side-effects of this are infertility, stunted mental development (such as learning disabilities), stunted growth and lower life expectancy. And those are just the mildest side effects. Severe developmental deficiencies, and significantly heightened risk of all kinds of diseases (such as cardiovascular diseases) are also common. The list of possible symptoms is really extensive. And the more the number of sex chromosomes varies from the normal, the more common and severe the symptoms are. The more severe the variation, the less likely it is for the person to even survive to adulthood.
In fact, the vast majority of pregnancies with sex chromosome disorders end in miscarriage or stillbirth.
But Bill Nye doesn't convey any of this to the viewer. Instead, he gives the impression that people with an abnormal number of sex chromosomes are just normal healthy everyday people that you meet every day, and wouldn't even recognize outwardly as being such.
Bill Nye's hypocrisy is also heavily criticized because in his original "Bill Nye the Science Guy" TV series there was an episode dealing with genders and sex chromosomes, which stated, clearly and repeatedly, that there are only two sexes, period. This segment was completely cut out from the Netflix re-release of the series.