In a new support document, Apple says not to close the cover of your MacBook when using a webcam cover. Doing so may damage the screen.
When you close the cover of your MacBook, the space between the screen and the keyboard is small, and the extra thickness of a webcam cover can damage the screen over time. If your cover is thicker than 0.1 mm (average thickness of printer paper), remove it before closing the cover.
Apple’s advice is to control access to the camera in System Preferences and the camera light to find out if the camera is active. Mac cameras are designed so that they cannot activate without the green light also turning on.
Control access to the camera
Apps and websites can use your camera to take photos or videos, and you can control their access.