XWayland has already supported system bell type functionality where the Wayland compositor implements XkbBellNotifyMask support. But now XWayland supports xdg-system-bell as that newer Wayland protocol for handling system bell functionality. Rather than making it necessarily ring an audible system bell on systems supporting it, the xdg-system-bell protocol could be implemented by Wayland compositors as a visual cue or other indicator that such an event was triggered.
The xdg-system-bell protocol was rolled out in October with Wayland Protocols 1.38 . It's quite open in the protocol for how compositors can implement the functionality:
"This requests rings the system bell on behalf of a client. How ringing the bell is implemented is up to the compositor. It may be an audible sound, a visual feedback of some kind, or any other thing including nothing.
The passed surface should correspond to a toplevel like surface role, or be null, meaning the client doesn't have a particular toplevel it wants to associate the bell ringing with. See the xdg-shell protocol extension for a toplevel like surface role."
In any event with this merge it's now the newest feature of XWayland.