OP means that the third sleeve/fourth connection point on the jack (the one responsible for mic data) isn't passed through, ergo the only connection to the recipient device is the output. In other words, it limits a TRRS jack to a TRS one.
Whatever OS you're using, you're not magically going to regain access to a physically disconnected signal.
My laptop recognizes it as an actual microphone. Unless some software is able to change the microphone selection to the internal microphone, it will just be listening to silence.
Not sure what you are using but on Windows I can set my "default" but each application can still individually select which input they want.
IE an untrusted process running should be able to pick the inbuilt mic.
Maybe linux has permissions around device inputs that can be used to stop this but if a person is worried their untrusted laptop might be listening to them then I suspect such a permission layer is already breached.
jraph is simply pointing out that a laptop likely has a built in mic which can still be surreptitiously used no matter what the user plugs in and says is their preference. Untrusted is untrusted.
_carbyau_'s interpretation is correct, I meant to say that if you don't trust your laptop, you can't block for sure its internal mic by plugging a fake external mic. An untrusted app could always select the internal mic.
Whatever OS you're using, you're not magically going to regain access to a physically disconnected signal.