Tab: Marketing > Notifications. Four Yes/No switches, all No by default, global only:

• Enable New Notifications Sound – plays a sound in the admin panel when a new order notification arrives.
• Enable New Notifications Side Popup – shows a toast in the corner of the admin screen. In the current version this fires on any device (not desktop-only) once the setting is Yes.
• Enable New Notifications Side Popup On Mobile – an additional toast trigger that only fires when the admin panel is opened on a mobile browser; turning this on together with the Side Popup switch can show the toast twice on mobile.
• Enable System Notifications – additionally asks the browser for permission to show native desktop/system notifications.

These only take effect while Enable Notifications is Yes and the admin user has the panel open (they listen for a live "order created" event).