I created this post so as not to put an off-topic post in the Anyone daily drive KDE? topic.
Hi @berninghausen,
Jimmy (@Akatama) and Cane (@TrekJunky) are right: I had to set up at least 2 virtual desktops to get the virtual desktops switcher icon (widget) on the panel.
These are the steps I took to add the virtual desktops ( I’m using KDE Plasma 5.27.8):
Open System Settings (Application Laucher → System Settings):