Created attachment 106297 [details] Self-explanatory screenshot of an ordinary settings window According to the KDE Plasma 5.10 release announcement, the option should be present in settings in KDE Plasma 5.10 and above. Or.. Am I missing something? The video on the KDE official YouTube channel showcased that function with a panel sticking to the left side. Actually, I can't verify if it does appear for a left-sided panel since Plasmashell crashes when I try to do so on my installation.
It's available in vertical panels.