I know you can mute a site by default but can you set the default to mute all tabs? This is a request from several of my customers.
There is currently no option built insider Edge insider browser that can do that but there is an extension that should do it.
Also there are other considerations:
you can use this flag:
Enables enforcement of a single media session having audio focus at any one time. Requires #enable-media-session-service to be enabled too. – Mac, Windows
in here: edge://flags/
use Media Autoplay Blocking feature to prevent multi media files from being played automatically.