I attending Montessori and enjoyed it, but this was 10+ years ago. We did not talk about the teacher's personal beliefs and politics, and there was no discussion of student gender or sexuality. It was focused on social and interpersonal development and academics. I understand some people believe discussing these sensitive topics is essential to student development, but I think it has made kids very uncomfortable and strayed too far from academics.
Despite what you've heard, they don't really talk about those things in public school either.
They absolutely do at least in CA starting in kindergarten
Discussion of gender seems to be pretty in-line with kindergarten education from what I remember 20 years ago. Hell, we even "voted" in the 1996 presidential election (I voted for the most attractive person, Bill Clinton).