Comment # 2 on bug 1178132 from Wolfgang Bauer

I had a look at the (upstream) source code, and the shortcut is clearly defined
there:
    d->actionMoreEffects = ac->addAction
(QStringLiteral("image_more_effects"));
    d->actionMoreEffects->setText (i18n ("&More Effects..."));
    connect (d->actionMoreEffects, &QAction::triggered, this,
&kpMainWindow::slotMoreEffects);
    ac->setDefaultShortcut (d->actionMoreEffects, Qt::CTRL + Qt::Key_M); 

(see
https://invent.kde.org/graphics/kolourpaint/-/blob/master/mainWindow/kpMainWindow_Image.cpp,
line#188 ff.)

So this should better be reported upstream at bugs.kde.org if it is considered
to be a problem.