Enter “dev” in the search bar and click on developer options, there you find both these options.
You click on the server name above the tree (if connected to the server) and then on the little pencil icon on the right (you need permissions to edit though, otherwise icon is not visible).
The following shortcuts apply to the global sound menu at the top:
Shift + LMB: mute everywhere, except the current selected server (also unmute on the selected server if muted) (my idea 
)
Alt + LMB: mute only on selected server
