SUMMARY
Steam provides Steam Overlay. In my Opinion, there should be Desktop Overlay, activating showing small, semi-transparent window, when fullscreen window/game are displayed. Programs could tell DE to display or not or give DE choice of displaying this window.

On this window will be shown DE related stuff. Most interesting could be tray items, so user could easily mute/unmute sound, response to chat (when playing game and chat on discord for example), etc. 

Also, fullscreen overlay with many options could been brings, when user click on icon of this small window or press keyboard shortcut.

STEPS TO REPRODUCE
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OBSERVED RESULT


EXPECTED RESULT


SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION