These people should be looking into spinning up Matrix servers if they want a private club with real privacy so bad.
It’s definitely a weird thing to constantly be upset about: “People can see what I posted in public when I post them publicly!”
It’s like complaining about people being able to take photos with you in the background in public. It’s a public space, there is no expectation of privacy.
If you want a private internet experience, you have to put some work in.