Convert notification-area applet to helper application
This applet use some functions that are deprecated and removed in GTK 4. Also it seems weird to have two applets that provides similar functionality...
This applet should be converted into helper application with well-known D-Bus name and should autostart when status-notifier creates
GDBusProxy. Helper application should convert old tray icons to status notifier items.
System Tray Protocol:
Something similar was done for KDE: