Wezterm has a utility for raising GUI system notifications, window:toast_notification(), which is a handy way to bring notifications to you that you might otherwise miss if the window is hidden or if a given tab is inactive.

However, on Linux, it's a far from ideal tool, at least under gnome-shell. (I don't know how it does on KDE or other desktop environments.) It raises the notification, but the notification never times out, even if you provide a timeout value (fourth argument to the function). This means that you have to manually dismiss the notification, which can be annoying, particularly if the notifications happen regularly.

So, I worked up my own utility.