He’s probably mixing up multiple stories.
California didn’t make it so that birth certificates don’t have a gender on them when you are born, but California did make it such that you can amend your birth certificate later on to change the sex or make it nonbinary, per a law passed in 2017 and implemented in 2018.
The idea of removing sex from birth certificates isn’t a law in California, but it was proposed a number of times; I remember that specifically because there was a thread on this on the Dope when PA proposed it a few years ago:
That law didn’t pass (although funnily enough when I tried to look it up I saw that articles from 2025 about PA lawmakers with the same proposal). But the idea of removing sex from birth certificates is what Maher was alluding to, and he’s certainly not lying about that being a thing that was getting pushed. Hell, go read the linked thread - plenty of people here defended the idea.