I'm running Ubuntu 18.04.3 LTS with kubuntu-desktop and SDDM, the KDE Plasma display manager.
I told accessibility to flash the window for terminal bell. (I also told it to use /usr/share/sounds/freedesktop/stereo/message click, which it entirely ignored in favour of ubuntu/stereo/bell, but I'm not too bothered about that right now. RIP stupid bell file, even if I had to reboot to clear some stupid cache.)
The accessibility flash works in various consoles I've tried: xterm, Eterm, rxvt, and even in Intellij and (bizarrely) gnome-terminal, yet when I use Konsole - KDE's own terminal - it does precisely nothing.
I know I can mess with xcalib and Konsole's notifications menu to tell it to flash all attached screens, but that's really not the point: shouldn't Konsole be something of a poster-boy - a well-behaved KDE application?
I make the beep by pressing backspace at an empty terminal prompt.