ibus Build-Depends on dbus-x11, presumably because
several automated tests explicitly invoke dbus-launch.

dbus-launch is poorly-understood legacy code and is best avoided. If
these test-cases want to start a temporary dbus-daemon, connect to it, do
some testing and then terminate it, it is better to invoke dbus-daemon
directly (which only requires the dbus-daemon package), using its
--fork, --print-address and --print-pid options: for example, search for 
dbus-daemon in
https://salsa.debian.org/debian/flatpak/-/blob/debian/trixie/tests/libtest.sh
for an example of doing this in a shell script.

See also <https://lists.debian.org/debian-devel/2016/08/msg00554.html>,
a mass bug filing in 2016 (at which point I think this dependency might
not have yet existed).

Thanks,
    smcv