The title is arguably a bit baity. I have not been keeping that much up with now now. I guess all the OSes that are out there right now have been out for at least a decade now, indeed. Redox, Haiku, Serenity, the Assembly ones, Qubes (is that really an OS, though?)...

I guess, this, how come, I mean. Isn't AI all about replacing developers? Now this is impossible? What kind of narrative are we collectively pushing?

But see https://github.com/jubalh/awesome-os

There are dozens and dozens of new operating systems listed here. Most are experiments -- what you might call hobby projects -- but there are some interesting ideas implemented among them.