SUMMARY First issue is that right-aligned buttons overflow beyond the dummy window's titlebar. Second thing is that dragging button from options list to the titlebar visually does nothing.. But saving the changes after each modification does the trick in the end. But coming back to the edit, the buttons are not there anyway. SOFTWARE/OS VERSIONS Linux/KDE Plasma: 5.14.8-arch1-1 64-bit (available in About System) KDE Plasma Version: 5.22.5 KDE Frameworks Version: 5.86.0 Qt Version: 5.15.2 ADDITIONAL INFORMATION
I'm on Plasma 5.23.1 now, and it's fixed for me.
Phew!