Even HTML5 web capturing works in a similar way. Once you give an site like Discord access to your microphone or screen it can pretty much access it whenever the page is open - granted it will show a little badge on screen by default.

A lot of users got tired of the on-screen badge being on all the time and probably set it to hidden (very easy to do) so not everyone is actually aware of when an HTML5 application is accessing a microphone/camera/screen.