SUMMARY If the computer has no battery (yes, notebooks and smartphones are not the only existing computing devices) and no screen whose brightness can be set by software and no bluetooth device, the applet can do nothing at all, but is still shown, which is not useful. STEPS TO REPRODUCE 1. Use an old-fashioned desktop PC OBSERVED RESULT There is an empty applet in your tray wasting space with which you can do nothing. EXPECTED RESULT The applet should not be shown if there is nothing which the user can see or do with it. If this should be too complicated, at least it should be possible to deactivate the applet in the corresponding system settings. SOFTWARE/OS VERSIONS Operating System: Debian GNU/Linux KDE Plasma Version: 5.23.2 KDE Frameworks Version: 5.86.0 Qt Version: 5.15.2 Kernel Version: 5.14.0-2-amd64 (64-bit) Graphics Platform: X11 Processors: 4 × Intel® Core™ i5-6500 CPU @ 3.20GHz Memory: 11,6 GiB of RAM Graphics Processor: Mesa Intel® HD Graphics 530 ADDITIONAL INFORMATION The summary is meant humorously. I am very happy about all your work!
You can disable entries in the System Tray using its configuration dialogue (click on the little up-arrow then click the button in the title bar of the pop-up). On my desktop PC the "Battery and Brightness" entry is "Shown when relevant" which means it is not shown in the System Tray. Does that not provide the functionality you need?
Thanks for the hint, I totally forgot about that. I still think, that in an ideal world, this manual process would be automated i.e. the applet would only be shown if there is something useful to do. That said, I won't implement it and if noone else plans to do it, the report can be closed. Thanks again!