Cortex deck plugs and Cortex trim plugs are designed to stay in place.
Plugs are sized with a slight interference fit between the cylinder and the installed plug
Plugs are made from the manufacturer deck boards so thermal expansion and contraction doesn't result in a plug being squeezed or being loose in the cylinder. Plugs grow and shrink at the same rate as the board does so the slight interference fit is maintained at all times.
As the screw is driven in, it is cutting the cylinder below the decking's surface the screw imparts a texture on the inside wall of the cylinder. This texture gives the plug a friction fit.
After the screw is driven to depth with the setting tool the plug is firmly driven into the cavity with a hammer. This compression drives air out from beneath the plug and seals screws head off from the elements.