It does happen, though I'm glad to learn it doesn't happen in your circles. As a former receptionist who could hear in the conference room of my office though the people inside didn't realize, the men absolutely did say much worse things when no women were in the room.

I went to a liberal arts college full of progressive and Democrats who openly disparaged conservatives. I witnessed often reprehensible behavior.

One time my husband called out a misogynistic comment in a friend group chat. He found out a year later calling out that behavior once is why he was never added to the males only chat. They didn't want to have to "watch what they say" around him. Men definitely do speak differently in situations where women are not present. Not all men, but plenty.