I don't have a Windows solution to the "mute everything for presentations" problem, but for anyone on macOS: option-click on the clock / notification section in the menu bar and you'll put yourself into Do Not Disturb mode. Option-click the clock again to disable.
The discoverability of that shortcut isn't great but it has become one of my favorite macOS features.
Amusingly, the first thing it does is put a big countdown clock on your screen, counting down the time till your "focus" ends. Otherwise it works pretty well.
The discoverability of that shortcut isn't great but it has become one of my favorite macOS features.