It's not redundant. I'd say it's wrong. If biology is how the body is working, biological sex should be the same as hormonal sex, which would be the same as someone's sex confirmation therapy is making it, not sex assigned at birth.

It is not implied to mean "biological sex" because that's not a term anyone used until anti-trans people made it up. It is only used rhetorically to imply their view is the one supported by science. It isn't.

So immediately jumping to "dogwhistle" every time you hear someone say something that's supposedly in this list of secret right-wing code words is kind of a disingenuous argument and you're just going to alienate people who then won't take you seriously in the future.

Dog whistles can become mainstream. It doesn't change the origin. Just because you hear it on TV sometimes doesn't mean that's the correct term. It was made up as a rhetorical argument to imply superiority. That's it.