My laptop has a build in camera cover that can be slid over the camera. I wonder if this is some sort of trick, like the cover is actually transparent from the inside.
Never seen one I'd actually trust for the mic, but I've seen a lot of Lenovos that have sliding covers for the camera.
I'm a little reluctant to put an adhesive slider on my MacBook because it closes pretty tight and I'm afraid the extra thickness would create a pressure point and cause damage over time.
In our scenario we are thinking about someone trying to sneak on you. But a jack mic cut off is not removing the internal microphone just putting the source to a different one. So if this person has access to your PC he coule surely access other sensors than the cut off jack