I recently updated Debian testing, and apper got an update (new version is 0.8.0-2). It changed the UI behavior, and doesn't show a system tray icon anymore, when there are pending updates (it shows a notification once and that's it). Is there a way to bring system tray icon back? It reminds that there are updates pending, and without it it's not obvious.

It seems Apper now provides an "Updater applet" instead, which is designed for use in Plasma Desktop. You'll need to add this to your panel or system tray - after which it should provide similar functionality.

There is a "Software Updater" applet indeed. But it can be added only to the panel. And it's always there even if there aren't any pending updates - which clutters the UI. How can put it into the system tray? I thought system tray is managed by the applications themselves and the user has no direct control over it. Prior behavior of Apper was perfect - icon in system tray when there are updates, and no UI when there aren't any. This applet isn't really a good substitution for the previous behavior.

If you right click on the hidden icons arrow > System Tray Settings > Display, then search the Extra Items section, do you see the Apper applet listed there? If so, check it and it should appear in your system tray.

shmerl wrote:There is a "Software Updater" applet indeed. But it can be added only to the panel. And it's always there even if there aren't any pending updates - which clutters the UI. How can put it into the system tray? I thought system tray is managed by the applications themselves and the user has no direct control over it. Prior behavior of Apper was perfect - icon in system tray when there are updates, and no UI when there aren't any. This applet isn't really a good substitution for the previous behavior.

IIRC, the "Software Updater" applet is set to "Always visible" by default.
Right-click on the small arrow on the right side of the system tray and choose "Systemtray Settings". In the left column click on "Entries" and you should get a list of all system tray items in the right column. Look for the "Software Updater" there and set it to "Auto". Then it should disappear if no updates are available and re-appear when there are some.

Great, thanks for the tips, I had no idea that one can place widgets into the system tray. This solves it.