I've just upgraded to 5.20 and the icons are slightly bigger than in the image. It doesn't look as harmonious as the Windows 10 sidebar, but the slight size increase makes a difference. All in all, it's an improvement over the previous list-style panel, because the information is easier to read.

Someone should dig out the relevant source code for you to fix it.

I'm sure a good PR will be well received :-)

The UI code for the system tray can be found here: https://invent.kde.org/plasma/plasma-workspace/-/tree/master... and the HiddenItemsView.qml is the part show on the screenshot. MR are always welcome.

> cellWidth: hiddenTasks.width / hiddenTasks.columns > cellHeight: hiddenTasks.height / hiddenTasks.rows

Looks like the window should default smaller to make the sizes reasonable, or whatever decides the columns/row counts needs some tweaking.