Maybe nobody says that exact thing, but people do often say things like “if you don’t like it you can fork it”, as a way of shutting down discussions.
I maintain forks that are frequently rebased on main/master with a few users. I have even suggested this as an action to people who wanted different features that I was not capable of maintaining.
However for many projects ‘just fork it’ is not a good faith suggestion, so it can’t be a blanket answer that applies to all FOSS.