Comment 2 for bug 1689297

Try using either

    octave -q -f --no-gui-libs add.m

or

    octave-cli -q -f add.m

This will run Octave without any initialization of the Qt toolkit, which is probably where these noisy warning messages are coming from. These messages are not generated by Octave, and there is probably not much Octave can do about silencing them as long as it is loading the Qt toolkit, which indirectly loads GTK and this buggy theme that is active on your system.