I recently installed Manjaro and am using the latest version of KDE available at the moment (5.20.3).

My configuration goal was to have a small panel across the top with the task manager and system tray and such, and a larger panel on the side with quick launch icons that would auto-hide.

After getting the new panel in place on the side, first I tried dragging icons from the application menu to the panel. With the first icon it created a launcher, but it wouldn't create any more, no matter how many times I tried to drag more icons to the panel. It would only create one launcher, one icon, on the panel and that's it.

Next I tried the Quick Launch widget. That allowed me to drag and add all the icons I wanted to the launcher, but it also had issues. Whenever I would right-click on an icon to bring up its context menu, such as being able to launch a private window with browsers, about a second after right-clicking on the icon the mouse cursor would pick up the icon as if I was trying to drag it, each and every time, making the quick launcher unusable. Right-click, wait a second, and then the cursor would just pick the icon up.

Next I tried dragging the icons onto the desktop which created links, and then dragging those links to the panel. That worked for the first three icons but then just like when dragging straight from the application menu, the panel just wouldn't accept any more. After dragging three icons from the desktop to the panel it wouldn't add any more.

Finally, I found something that worked. I right-clicked each and every icon I wanted and chose "+Add to Panel (Widget)" which added the icons to the top panel as widgets. Then I dragged those icons from the top panel onto the desktop where they remained launcher widgets instead of becoming links. Then I was able to drag the widgets from the desktop to the side panel. It seems like a lot of work to do something so simple.

I'm not sure if this is a bug but it seems like one to me.