A recent IBus notification is more verbose (but still, outdated):
IBus should be called from the desktop session in Wayland. For KDE, you can launch ‘systemsettings5’ utility and go to “Input Devices” → “Virtual Keyboard” section and select “IBus Wayland” icon and click “Apply” button to configure IBus in Wayland. For other desktop sessions, you can copy the ‘Exec=’ line in org.freedesktop.IBus.Panel.Wayland.Gtk3.desktop file to a configuration file of the session. Please refer each document about the “Wayland input method” configuration. Before you configure the “Wayland input method”, you should make sure that QT_IM_MODULE and GTK_IM_MODULE environment variables are unset in the desktop session.
IBus 1.5.32~rc2-1, Plasma 6.34, Ubuntu 25.04.